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