Log Message:
Update to 4.0.0

Changelog:
4.0.0
Major Enhancements
    Drop ruby 2.3 (#7454)
    Drop support for Ruby 2.1 and 2.2 (#6560)
    Drop support for older versions of Rouge (#6978)
    Drop support for pygments as syntax-highlighter (#7118)
    Drop support for Redcarpet (#6987)
    Drop support for rdiscount (#6988)
    Drop support for jekyll-watch-1.4.0 and older (#7287)
    Incorporate relative_url filter in link tag (#6727)
    Upgrade kramdown dependency to v2.x (#7492)
    Upgrade jekyll-sass-converter to v2.x - Sassc + sourcemaps (#7778)
    Upgrade i18n to v1.x (#6931)
    Add Jekyll::Cache class to handle caching on disk (#7169)
    Cache converted markdown (#7159)
    Cache: Do not dump undumpable objects (#7190)
    Cache matched defaults sets for given parameters (#6888)
    Ignore cache directory (#7184)
    Add Site#in_cache_dir helper method (#7160)
    Remove 'cache_dir' during jekyll clean (#7158)
    Cache parsed Liquid templates in memory (#7136)
    Only read layouts from source_dir or theme_dir (#6788)
    Allow custom sorting of collection documents (#7427)
    Always exclude certain paths from being processed (#7188)
    Remove Jekyll::Utils#strip_heredoc in favor of a Ruby > 2.3 built in (#7584)
    Incorporate relative_url within post_url tag (#7589)
    Remove patch to modify config for kramdown (#7699)

Minor Enhancements
    Enhance --blank scaffolding (#7310)
    Use jekyll-compose if installed (#6932)
    Disable Liquid via front matter (#6824)
    Configure cache_dir (#7232)
    ISO week date drops (#5981)
    Fix custom 404 page for GitHub pages (#7132)
    Load config file from within current theme-gem (#7304)
    Suggest re-running command with --trace on fail (#6551)
    Support for binary operators in where_exp filter (#6998)
    Automatically load _config.toml (#7299)
    Add vendor folder to a newly installed site's .gitignore (#6968)
    Output Jekyll Version while debugging (#7173)
    Memoize computing excerpt's relative_path (#6951)
    Skip processing posts that can not be read (#7302)
    Memoize the return value of Site#documents (#7273)
    Cache globbed paths in front matter defaults (#7345)
    Cache computed item property (#7301)
    Cleanup Markdown converter (#7519)
    Do not process Liquid in post excerpt when disabled in front matter (#7146)
    Liquefied link tag (#6269)
    Update item_property to return numbers as numbers instead of strings (#6608)
    Use .markdown extension for page templates (#7126)
    Add support for *.xhtml files (#6854)
    Allow i18n v0.9.5 and higher (#7044)
    Ignore permission error of /proc/version (#7267)
    Strip extra slashes via Jekyll.sanitized_path (#7182)
    Site template: remove default config for markdown (#7285)
    Add a custom inspect string for StaticFile objects (#7422)
    Remind user to include gem in the Gemfile on error (#7476)
    Search Front matter defaults for Page objects with relative_path (#7261)
    Lock use of tzinfo gem to v1.x (#7521, #7562)
    Utilize absolute paths of user-provided file paths (#7450)
    Detect nil and empty values in objects with where filter (#7580)
    Initialize mutations for Drops only if necessary (#7657)
    Reduce Array allocations via Jekyll::Cleaner (#7659)
    Encode and unencode urls only as required (#7654)
    Reduce string allocations with better alternatives (#7643)
    Reduce allocations from Jekyll::Document instances (#7625)
    Add type attribute to Document instances (#7406)
    Reduce allocations from where-filter (#7653)
    Memoize SiteDrop#documents to reduce allocations (#7697)
    Add PathManager class to cache interim paths (#7732)
    Remove warnings and fixes for deprecated config (#7440)
    Delegate --profile tabulation to terminal-table (#7627)

Bug Fixes
    Security: fix include bypass of EntryFilter#filter symlink check (#7226)
    Theme gems: ensure directories aren't symlinks (#7419)
    Add call to unused method validate_options in commands/serve.rb (#7122)
    Check if scope applies to type before given path (#7263)
    Document two methods, simplify one of the methods (#7270)
    Check key in collections only if it isn't "posts" (#7277)
    Interpolate Jekyll::Page subclass on inspection (#7203)
    Measure the no. of times a template gets rendered (#7316)
    Reduce array traversal in Jekyll::Reader (#7157)
    Re-implement handling Liquid blocks in excerpts (#7250)
    Documents should be able to render their date (#7404)
    Fix Interpreter warning from Jekyll::Renderer (#7448)
    Loggers should accept both numbers and symbols (#6967)
    Replace regex arg to :gsub with a string arg (#7189)
    Dont write static files from unrendered collection (#7410)
    Excerpt handling of custom and intermediate tags (#7382)
    Change future post loglevel to warn to help user narrow down issues (#7527)
    Handle files with trailing dots in their basename (#7315)
    Fix unnecessary allocations via StaticFileReader (#7572)
    Don't check if site URL is absolute if it is nil (#7498)
    Avoid unnecessary duplication of pages array (#7272)
    Memoize Site#post_attr_hash (#7276)
    Memoize Document#excerpt_separator (#7569)
    Optimize Document::DATE_FILENAME_MATCHER to match valid filenames (#7292)
    Escape valid special chars in a site's path name (#7568)
    Replace name in Page#inspect with relative_path (#7434)
    Log a warning when the slug is empty (#7357)
    Push Markdown link refs to excerpt only as required (#7577)
    Fix broken include_relative usage in excerpt (#7633)
    Initialize and reset glob_cache only as necessary (#7658)
    Revert memoizing Site#docs_to_write and #documents (#7684)
    Backport #7684 for v3.8.x: Revert memoizing Site#docs_to_write and refactor \ 
#documents (#7689)
    Backport #7213 and #7633 for v3.8.x: Fix broken include_relative usage in \ 
excerpt (#7690)
    Don't read symlinks in site.include in safe mode (#7711)
    Replace String#=~ with String#match? (#7723)
    Update log output for an invalid theme directory (#7679)
    Remove configuration of theme sass files from Core (#7290)
    Actually conditionally include liquid-c (#7792)
    Test number_like regex on stringified property (#7788)

Development Fixes
    Upgrade liquid-c to v4.0 (#7375)
    Bump RuboCop to v0.71.0 (#7687)
    Target Ruby 2.4 syntax (#7583)
    Fix: RuboCop offenses (#7769)
    Use communicative method parameters (#7566)
    Scan assert_equal methods and rectify any offenses with a custom RuboCop cop \ 
(#7130)
    CI: Test with Ruby 2.6 (#7438)
    CI: Test with Ruby 2.6 on AppVeyor (#7518)
    CI: Update RuboCop config (#7050)
    CI: Add a script to profile docs (#7540)
    CI(Appveyor): shallow clone with 5 last commits (#7312)
    CI: Test with oldest and latest Ruby only (#7412)
    CI: Update excludes for CodeClimate Analyses (#7365)
    CI: Lock Travis to Bundler-1.16.2 (#7144)
    CI: Bump tested version of JRuby to 9.2.7.0 (#7612)
    CI: Do not install docs on updating gems on Travis (#7706)
    Update gemspec (#7425)
    deps: relax version constraint on classifier-reborn gem (#7471)
    deps: update yajl-ruby (#7278)
    deps: bump yajl-ruby to v1.4.0 (#6976)
    Create symlink only if target is accessible (#7429)
    Switch to :install_if for wdm gem (#7372)
    Add cucumber feature to test include_relative tag (#7213)
    Small benchmark refactoring (#7211)
    Fix incorrectly passed arguments to assert_equal (#7134)
    fix up refute_equal call (#7133)
    Fix RuboCop offences in test files (#7128)
    Use assert_include (#7093)
    Remember to release docs gem (#7066)
    Useless privates removed (#6768)
    Load Rouge for TestKramdown (#7007)
    Update instructions for releasing docs Gem (#6975)
    We are not using Ruby 2.2 anymore (#6977)
    Remove unnecessary Jekyll::Page constant (#6770)
    Remove unused error class (#6511)
    Add a Cucumber feature for post_url tag (#7586)
    Generate a "TOTAL" row for build-profile table (#7614)
    Refactor Jekyll::Cache (#7532)
    Store list of expected extnames in a constant (#7638)
    Profile allocations from a build session (#7646)
    Update small typo in contributing.md (#7671)
    Remove override to Jekyll::Document#respond_to? (#7695)
    Update TestTags in sync with Rouge v3.4 (#7709)
    Use regexp to filter special entries (#7702)
    Reduce Array objects generated from utility method (#7749)
    Update mime.types (#7756)
    Replace redundant Array#map with Array#each (#7761)
    Reduce allocations by using #each_with_object (#7758)
    Memoize fallback_data for Drop (#7728)
    Use String#end_with? to check if entry is a backup (#7701)

Documentation
    Refactor docs (#7205)
    Add a link to Giraffe Academy's tutorial (#7325)
    Do not advise users to install Jekyll outside of Bundler (#6927)
    Remove documentation for using Redcarpet (#6990)
    Install Docs that Work on MacOS 10.14 (#7561)
    Add Installation Instructions for Ubuntu (#6925)
    Don't prompt for sudo when installing with Ubuntu WSL (#6781)
    Installation instructions for Fedora (#7198)
    Update Windows install docs (#6926)
    List all standard liquid filters (#7333)
    List all static files variables (#7002)
    Improve how to include Rouge stylesheets (#7752)
    Mention CommonMark plugins (#7418)
    Add TSV to list of supported _data files. (#7168)
    How to deploy using pre-push git hook (#7179)
    Hosting with AWS Amplify (#7510)
    CircleCI deployment through CircleCI v2 (#7024)
    GitHub Pages: use themes from other repos (#7112)
    Document page.dir and page.name (#7373)
    Document custom tag blocks (#7359)
    Document converter methods (#7289)
    Document {{ page.collection }} (#7430)
    Document Jekyll Filters with YAML data (#7335)
    Document where Jekyll looks for layouts in a site (#7564)
    plugin: liquid tag jekyll-flickr (#6946)
    plugin: jekyll-target-blank (#7046)
    plugin: json-get. (#7086)
    plugin: jekyll-info (#7091)
    plugin: jekyll-xml-source (#7114)
    plugin: jekyll-firstimage filter (#7127)
    plugin: CAT (#7011)
    Resources: Statictastic (#7593)
    Resources: Bonsai Search (#7543)
    Resources: Formspark (#7601)
    Resources: Jekpack(#7598)
    Resources: formX (#7536)
    Resources: 99inbound's Jekyll post (#7348)
    Resources: CloudSh (#7497)
    Community: DEV Community's Jekyll tag (#7139)
    Showcase: developer.spotify.com (#7217)
    Showcase: Isomer (#7300)
    Add version number for group_by_exp doc (#6956)
    Updated nginx configuration for custom-404-page documentation (#6994)
    Clarify definition of 'draft' (#7037)
    _drafts need to be contained within the custom collection directory (#6985)
    Updated to supported version (#7031)
    Add Hints for some Improved Travis Config in Doc (#7049)
    Update travis-ci.md to point out "this is an example Gemfile" (#7089)
    Instructions to view theme’s files under Linux (#7095)
    Use a real theme in the example (#7125)
    Update docs about post creation (#7138)
    Initialize upgrading doc for v4.0 (#7140)
    Add version badge for date filters with ordinal (#7162)
    Corrected sample usage of postfiles (#7181)
    Resolve "Unable to locate package ruby2.4" error (#7196)
    Correct stylesheet url in tutorial step 7 (#7210)
    Removes quotes from markdown for assets (#7223)
    Clarified front matter requirement (#7234)
    Explicit location of where to create blog.html (#7241)
    Reference the build command options that allows multiple config files (#7266)
    Add more issue template(s) and pull request template (#7269)
    Suggest sites use OpenSSL instead of GnuTLS for their site's CI (#7010)
    Fix broken Contributors link in README.markdown (#7200)
    Add title tag to item in RSS template (#7282)
    Add link tag to item in RSS template (#7291)
    Remove redundant instruction comment (#7342)
    Textile is only supported through a converter plugin (#7003)
    Add recursive navigation tutorial (#7720)
    Remove installation instructions with Homebrew (#7381)
    Fix dead link and misleading prose (#7383)
    Fix content management section (#7385)
    Apply ruby official guide documents (#7393)
    Fix group_by_exp filter example (#7394)
    Remove alt attribute from a tags (#7407)
    Fix BASH code-block in ubuntu.md (#7420)
    zlib is missing (#7428)
    Fixed unnecessary aticles and pronouns (#7466)
    Store SSL key and cert in site source (#7473)
    Fix typo in tutorial for converting existing site (#7524)
    Check if var exists before include tag (#7530)
    Clarify docs on collections regarding the need for front matter (#7538)
    Fix incorrect Windows path in themes.md (#7525)
    Addresses bundle not found. (#7351)
    Update the contribution docs for draft pull requests (#7619)
    Data file section adds TSV (#7640)
    Indicate where the _sass folder is by default (#7644)
    Docs: add version tags to new placeholders (#5981) for permalinks (#7647)
    Solve "GitHub Page build failure" in 10-deployment.md (#7648)
    fix link to Site Source config (#7708)
    Introduce frontmatter in step 2 (#7704)
    Add @ashmaroli to Core Team listing (#7398)
    Lnk to Tidelift in site's footer (#7377)
    Link to OpenCollective backing (#7378
    Link to sponsor listing in README (#7405)
    Adjust team page listings (#7395)
    Updates to CODE OF CONDUCT (v1.4.0) (#7105)
    More inclusive writing (#7283)
    Update Ruby version used in Travis-CI example (#7783)
    Documentation for binary operators in where_exp (#7786)
    Adding SmartForms as Forms service (#7794)

Site Enhancements
    Better Performance (#7388)
    Add some minor improvements to image loading in Showcase page (#7214)
    Simplify assigning classname to docs' aside-links (#7609)
    Simplify couple of includes in the docs site (#7607)
    Avoid generating empty classnames (#7610)
    Minimize rendering count (#7343)

Release
    Release post for v4.0.0 beta1 (#7716)
    Release post for v4.0.0.pre.alpha1 (#7574)
    Release post for v3.8.0 (#6849)
    Release post for v3.6.3, v3.7.4 and v3.8.4 (#7259)
    Post: v4.0 development (#6934)