R1:e24a6acf58fc

Multiline Highlighting in Diffusion

Summary:
I added multiline highlighting with the syntax:

http://site/path/to/file$from-to

NOTE: you can reverse the from and to

Test Plan: Open a file in diffusion and attempt to highlight multiple lines

Reviewers: epriestley

CC: aran, epriestley

Differential Revision: https://secure.phabricator.com/D1693