Minor improvements to Diviner layout

Summary:

• Render functions as func() for consistency/clarity.
• Sort articles first.
• Sort case insensitively.
• Label the "no group" symbols.

Test Plan: Regenerated and examined docs.

Reviewers: btrahan, chad

Reviewed By: chad

CC: aran

Differential Revision: https://secure.phabricator.com/D8480