Clean up some more Diviner stuff

Summary:
Ref T988.

• Render "Implements:" as tags, too.
• Minor CSS tweak to tags in property lists.
• Add a bunch of group patterns to the Phabricator book.
• Fix some stuff with how hashes are computed and cached.
• Minor tweak to reuse the Diviner engine for slightly improved performance.

Test Plan: Regenerated and looked at documentation.

Reviewers: chad

Reviewed By: chad

CC: aran

Maniphest Tasks: T3811, T988

Differential Revision: https://secure.phabricator.com/D6912