ANN: CommonMark 0.21

I have released version 0.21 of the CommonMark spec
as well as versions 0.21.0 of cmark, the C reference implementation
and commonmark.js, the JavaScript reference implementation.

Changelogs can be found at the links provided.

This is a fairly major update to the spec, with a completely rewritten spec for raw HTML blocks and new tab handling.

Both reference implementations have an option for a “safe mode,” in which raw HTML is suppressed and potentially dangerous link URLs are removed.

cmark has a new LaTeX renderer.