Commonmarker 1.0 switches to Rust implementation

[dentarg]

Noticed that Commonmarker 1.0 will switch to use https://github.com/kivikakk/comrak (https://docs.rs/comrak) instead of https://github.com/github/cmark-gfm, saving some interesting links

• Migrate to magnus/rb_sys gjtorikian/commonmarker#194
• Migrate to comrak/Rust gjtorikian/commonmarker#185
• Implement native syntax highlighting gjtorikian/commonmarker#209
• https://github.com/gjtorikian/commonmarker#commonmarker
• https://github.com/kivikakk/comrak
• https://rubygems.org/gems/commonmarker/versions
• Will the cmark-gfm branch continue to be maintained for awhile? gjtorikian/commonmarker#207

Maybe there will be some new features we can make use of? Thinking of syntax highlighting

We can close this issue once we use 1.0

[dentarg]

On the topic of Rust, there's gjtorikian/html-pipeline#368

This completes one of the blocking items for a v3 release: migrating to Selma. Selma's process for parsing html uses lol-html, a Rust library, as its underlying mechanism. It operates purely on CSS selectors, and has a few advantages over the current Nokogiri based mechanism. Namely, in the current systen, text is parsed over multiple times. Each NodeFilter runs its set of CSS selectors synchronously. lol-html, on the other hand, parses the text once, compiles its CSS selectors, and more efficiently allows for text manipulation.