Add syntax highlight to diffusion.

Summary:
use XHPAST parser to parse the file, and generate a table for
the code to highlight it. This is part of the task of "Port Diffusion's
Browse File view to Phabricator".

Test Plan:
browse file, try commit version, line number functionality.

Reviewed By: epriestley
Reviewers: epriestley
CC: epriestley
Differential Revision: 83