Log Message:
Update to 2.1.0

Changelog:
2.1.0
Changes
    2 minor change:
        Enable the use of extension gems in the kramdown binary through the new \ 
-x/--extension options (issue #569 by Ashwin Maroli)
        Allow using the Rouge plaintext lexer with the :guess_lang highlighting \ 
option (issue #572 and pull request #573 by Ashwin Maroli)

    1 bug fix:
        Fix problem with frozen string when using a codespan inside a table \ 
(issue #571 by Matijs van Zuijlen)

2.0.0
Changes
    3 major changes:
        Require at least Ruby 2.3 (fixes #557 by Matt Schreiber)
        Rouge is the new default syntax highlighter instead of Coderay
        Kramdown::Utils::OrderedHash has been removed in favor of Hash
        The following extension have been moved into their own repository and \ 
Rubygem:
            GFM parser
            PDF converter
            coderay syntax highlighter
            mathjaxnode math engine
            sskatex math engine
            katex math engine
            ritex math engine
            itex2mml math engine

    4 minor changes:
        Allow HTML5 style attribute values without quotes for HTML parser (issue \ 
#522 and pull request #523 by Dan Allen)
        Guessing of the syntax highlighting language with rouge is now only \ 
performed if the guess_lang option is set
        Paragraphs with a single image can now be rendered as a <figure> \ 
element by specifying the standalone IAL reference (fixes issues #48 by Gilbert \ 
Townshend and #98 by Luca Barbato)
        Add option footnote_prefix for avoiding duplicate IDs when rendering \ 
multiple documents (fixes issue #483 by Peter Poole)

    3 bug fixes:
        Add support for single backslash variant of hard line break to the \ 
(extracted) GFM parser (issue #519 and pull request #520 by Dan Allen)
        Don’t use the “plaintext” lexer of rouge
        Fix updating IAL references so that they get handled correctly