Added linting policies and tool.

Summary: This sets up linting policies and adds the cslint tool to the repository.  The linting tool alerts you to various policy issues when you do `arc diff`.

Test Plan: Apply the patch.  Modify a file in Tychaia.ProceduralGeneration and then do `arc lint`.  It should tell you about various policy issues, including issues around `ZoomType` (where we've defined more than one class in a single file).

Reviewers: Sabre070, jrhodes

Reviewed By: jrhodes

Maniphest Tasks: T7, T16

Differential Revision: http://code.redpointsoftware.com.au/D23