Summary: Depends on D20538. Ref T13291. We now recognize full source URIs, but encoding full URIs isn't super human-friendly and we can't do stuff like relative links with them. Add `{src ...}` as a way to get to this behavior that supports options and more flexible syntax.
Test Plan: {F6463607}
Reviewers: amckinley
Reviewed By: amckinley
Maniphest Tasks: T13291
Differential Revision: https://secure.phabricator.com/D20539
