Furigana/Ruby Support

[xelivous]

It would be nice to have ruby/furigana support as an addition to extension.cjk functionality or otherwise. The only alternative in markdown at the moment is to do the full blown html syntax which can be a little cumbersome and hard to read when doing it across a full document. This is a fairly core component of japanese/chinese when writing for a possibly younger audience or when using more obscure kanji/etc that aren't frequently seen. I only have experience with writing japanese text so I don't know how annoying certain options listed below would be with chinese IMEs.

ex: <ruby>絵文字<rp>(</rp><rt>えもじ</rt><rp>)</rp></ruby> -> 絵文字(えもじ)

Some example syntaxes:

1. [絵文字(えもじ)]
   • Would probably have to special case links with parenthesis inside of the brackets which isn't ideal.
   • ex: [link (test)](#url) should be link (test)
   • and you would have to do [[link (test)]](#url) to get the ruby link(test)
2. [絵文字]{えもじ}
3. [絵文字]《えもじ》
4. [絵文字]【えもじ】 or 【絵文字】《えもじ》 etc
5. ｜絵文字《えもじ》
   • This is the syntax used by the popular japanese webnovel platform narou. It uses a full-width pipe character instead of the half-width "normal" pipe (| vs ｜). It's possible to omit the ｜ in narou in certain cases if you're applying furigana to kanji exclusively where it will backtrack until it finds the first non-kanji character but it might not be worth implementing it this way in a general multi-language markdown parser.
   • Aozora Bunko uses this exact format as well, with the option to omit the ｜.

Example 5 makes the most sense for japanese-specific prior use, but might not make sense for chinese text or general usage.