[ANN] kramdown 2.0.0 released

## About kramdown

kramdown (sic, not Kramdown or KramDown, just kramdown) is a *free*
MIT-licensed [Ruby](http://www.ruby-lang.org) library for parsing a
superset of Markdown.

It is completely written in Ruby, supports standard Markdown (with some
minor modifications) and various extensions that have been made popular
by the PHP Markdown Extra package and Maruku.

Homepage for installation instructions and documentation:
   https://kramdown.gettalong.org

## kramdown 2.0.0 released

This is a major release with breaking changes!

The most notable changes are that Ruby 2.3 is now required, Rouge is
the new default syntax highlighter and that several extension have been
extracted to their own repository and Rubygem.

All extracted extensions are now officially **unmaintained** - if
anybody wants to step in, please [contact me](mailto:t_leitner@gmx.at).

There are also some minor changes and bug fixes, most notable:

* Paragraphs with a single image can now be rendered as `<figure>`
  elements.

* Footnote IDs can now be made unique using the new option
  `footnote_prefix`. Together with the exposed count of footnotes it is
  now possible to render multiple documents into one output file:

  ~~~ ruby
  require 'kramdown/document'
  total_footnotes = 0
  documents = [
    "footnote[^a][^a]\n\n[^a]: My note\n[^b]: another (ignored) note",
    "footnote[^a][^a]\n\n[^a]: My note\n[^b]: another (ignored) note",
    "footnote[^a][^a]\n\n[^a]: My note\n[^b]: another (ignored) note",
  ]

  documents.each do |document|
    options = {footnote_nr: total_footnotes + 1, footnote_prefix: total_footnotes + 1}
    document = Kramdown::Document.new(document, options)
    puts document.to_html
    total_footnotes += document.root.options[:footnote_count]
  end

···

~~~

## 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](https://github.com/kramdown/parser-gfm)
    - [PDF converter](https://github.com/kramdown/converter-pdf)
    - [coderay syntax highlighter](https://github.com/kramdown/syntax-coderay)
    - [mathjaxnode math engine](https://github.com/kramdown/math-mathjaxnode)
    - [sskatex math engine](https://github.com/kramdown/math-sskatex)
    - [katex math engine](https://github.com/kramdown/math-katex)
    - [ritex math engine](https://github.com/kramdown/math-ritex)
    - [itex2mml math engine](https://github.com/kramdown/math-itex2mml)

* 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

[#519]: https://github.com/gettalong/kramdown/issues/519
[#520]: https://github.com/gettalong/kramdown/pull/520
[#522]: https://github.com/gettalong/kramdown/issues/522
[#523]: https://github.com/gettalong/kramdown/pull/523
[#557]: https://github.com/gettalong/kramdown/issues/557
[#48]: https://github.com/gettalong/kramdown/issues/48
[#98]: https://github.com/gettalong/kramdown/issues/98
[#483]: https://github.com/gettalong/kramdown/issues/483

Cheers,
  Thomas

Hello,

  Congrats to the kramdown 2.0 release. Awesome!

   FYI: For more kramdown goodies, see the Awesome Kramdown page [1] -
a collection about all things kramdown - the converter for
(structured) text with formatting markup in markdown conventions
incl. Q&A with Thomas Leitner, writing tips & tricks, many addons and
tools and much more.

   Anything missing? Let us know.

   Cheers. Prost.

[1] https://github.com/mundimark/awesome-kramdown