Update look of Diviner docs index
Merge branch 'master' of github.com:facebook/phabricator
Diviner CSS, layout updates

Summary: Moves book view to use PHUIDocument, fix some other spacing issues.

Test Plan: Review a number of pages in Diviner.

Reviewers: epriestley

Reviewed By: epriestley

CC: Korvin, aran

Differential Revision: https://secure.phabricator.com/D6925