Summary:
Move Diffusion to be hovercard-ready, and expand our ability to resolve commit references.
- Link unqualified hashes of 7 characters or more which match a commit.
- Link qualified hashes of 5 characters or more which match a commit.
- Support `{...}` syntax.
Test Plan: {F33896}
Reviewers: chad, vrana
Reviewed By: vrana
CC: aran
Differential Revision: https://secure.phabricator.com/D5121
