Export code block language from Remarkup
Summary:
When highlighting a block of code, annotate the block with the
language that was used.
Test Plan:
Load a Differential page with code blocks in comments;
examine DOM.
Reviewers: epriestley
Reviewed By: epriestley
CC: aran, Korvin
Maniphest Tasks: T1602
Differential Revision: https://secure.phabricator.com/D3282