Allow full anchors in remarkup object names

Summary: Remarkup object names require #1 for linking to comments which is not
very intuitive.

Test Plan:

D1558#4e01328c
D1558#1
D1558#comment-1

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, epriestley

Differential Revision: https://secure.phabricator.com/D1565