Enable use of remarkup literal block
Summary:
D1293 adds support for a literal block in remarkup. This diff enables
it in phabricator with a few basic rules (for line breaks, escaping HTML,
and linkifying URLs).
Test Plan: Tested in sandbox
Reviewers: epriestley, jungejason
Reviewed By: epriestley
CC: aran, epriestley
Differential Revision: https://secure.phabricator.com/D1297