Allow lines to be specified as comma delimited number ranges for arc browse

Summary: Ref T5971. We lose validation of the line ranges, but I don't think that's a huge issue.

Test Plan: Ran arc browse README, arc browse README:3, and arc browse README:3,6-7

Reviewers: btrahan, epriestley, Blessed Reviewers

Reviewed By: epriestley, Blessed Reviewers

Subscribers: epriestley, Korvin

Maniphest Tasks: T5971

Differential Revision: https://secure.phabricator.com/D10352