Multi-line highlighting in Diffusion.

Summary: Currently, Diffusion supports highlighting of line ranges passed in the URI. It would be helpful to be able to highlight multiple line ranges.

Test Plan: Accessed directly via URL in my sandbox. Seems to work. I'm not sure what other components use this functionality, but this change should be backwards compatible.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D2921