Switch rustdoc to Common Markdown

[brson]

Assuming this takes off it's probably best to be on the right side of history: http://standardmarkdown.com/. Probably easiest to just make hoedown conformant.

[Gankra]

While I agree in principle, from their FAQ:

The current version of the Standard Markdown spec is complete (two years in the making!), but provisional pending public feedback, testing, and evaluation.

So I'm not sure if this is immediately appropriate. Should I log an issue against hoedown regardless?

[Gankra]

Being tracked by Hoedown at: hoedown/hoedown#119

[Gankra]

Moved to http://commonmark.org/

[RasmusWL]

Title should be change to CommonMark as well.

FYI: Hoedown is almost done with their implementation.

[steveklabnik]

I'm pulling a massive triage effort to get us ready for 1.0. As part of this, I'm moving stuff that's wishlist-like to the RFCs repo, as that's where major new things should get discussed/prioritized.

This issue has been moved to the RFCs repo: rust-lang/rfcs#620