add markdown parsing support with internal hyperlink detection for doc comments

[andrewrk]

zig/lib/std/special/docs/main.js

Lines 845 to 848 in cdaaf7c

	function markdown(mdText) {
	// TODO implement more
	return escapeHtml(mdText);
	}

I labeled this a contributor friendly issue, however, there are some restrictions on the markdown parsing:

• we should look for internal documentation hyperlinks in the doc comments (this can be a separate contribution)
• no npm or third party modules. We'll have our own custom minimal implementation. It's fine, don't worry about it.

[strangebug]

Hello,

Concerning this issue, the documentation in the javascript specify [[std;format.fmt]] as inner link format
https://github.com/ziglang/zig/blob/master/lib/std/special/docs/main.js#L1480

It is the intended format ?