R1:4adf55919c75

Port Diviner Core to Phabricator

Summary:
This implements most/all of the difficult parts of Diviner on top of Phabricator instead of as standalone components. See T988. In particular, here are the things I want to fix:

**Performance** The Diviner parser works in two stages. The first stage breaks source files into "Atoms". The second stage renders atoms into a display format (e.g., HTML). Diviner currently has a good caching story on the first step of the pipeline, but zero caching in the second step.