Disallow "{", "}" and "#" in Project monograms
Summary: Currently, mentioning two projects in a block ({#a} {#b}) produces an overzealous parse. Forbid these characters in project monograms.
Test Plan: Got correct markup.
Reviewers: btrahan, dctrwatson, chad
Reviewed By: chad
CC: aran
Differential Revision: https://secure.phabricator.com/D8141