Add an option to support CommonMark or support it by default

[cirosantilli]

You can check incompatibilities with:

./test/spec_tests.py --program kramdown

The problem is that now their normalization is broken so too many tests fail, so I'll keep a list of actual discrepancies here until the normalization gets fixed:

• invalid entity not converted to U+FFFD https://github.com/jgm/CommonMark/blob/b28c97c9b8af266d4f12deb5febcf28807d9f5c6/spec.txt#L4080

[gettalong]

kramdown is not commonmark. If you want a Ruby parser for CommonMark, write a parser for the kramdown library or write a standalone library.

[cirosantilli]

Sure, if I wanted a strict CommonMark parser I wouldn't be using Kramdown.

What I recommend is a gradual move towards CommonMark syntax, starting from the edge cases. Libraries that don't make this move are more likely to die in the long run. E.g.: if GitHub pages started supporting a CommonMark compiler I'd switch to it, which is the reason why I currently use Kramdown.

Of course, maybe it's not worth making that move from where Kramdown stands today given other implementations.

[Tuckie]

At the very least, having a CommonMark flavored markdown option might not be a bad idea...

[ghost]

For anyone using GitHub Pages, you can simply add this to _config.yml:

markdown: CommonMarkGhPages

you dont even have to declare the plugin in _config.yml as its activated by
default:

http://github.com/github/pages-gem/blob/fb5c3f2/lib/github-pages/plugins.rb#L9

reference:

http://github.com/github/jekyll-commonmark-ghpages