Log Message:
Update ruby-redcarpet to 3.3.1.

pkgsrc change:

* Add support for pkg_alternatives.
* Allow build on Ruby 2.2.

Version 3.3.1

* Include the Redcarpet::CLI's file in the gemspec to make it available when
  downloading.

Version 3.3.0

* Fix the stripping of surrounding characters that should be removed during
  anchor generation.

* Provide a Redcarpet::CLI class to create custom binary files.

* Relying on Ruby's OptionParser, it's now straightforward to add new options,
  rely on custom render objects or handle differently the rendering of the
  provided files.

* Undeprecate the compatibility layer for the old RedCloth API.

* This layer actually ease the support of libraries supporting different
  Markdown processors.

* Strip out style tags at the HTML-block rendering level when the :no_styles
  options is enabled ; previously they were only removed inside paragraphs.

* Avoid parsing images when the given URL isn't safe and the :safe_links_only
  option is enabled.

  Alex Serban

* Avoid parsing references inside fenced code blocks so they are now kept in
  the code snippet.

  David Waller

* Avoid escaping table-of-contents' headers by default. A new :escape_html
  option is now available for the HTML_TOC object if there are security
  concerns.

* Add the lang- prefix in front of the language's name when using :prettify
  along with :fenced_code_blocks.

* Non-alphanumeric chars are now stripped out from generated anchors (along
  the lines of Active Support's #parameterize method).