Return $this from setter methods
Summary: Return $this from setter methods for consistency. I started writing a linter rule to detect this, but I don't think it is trivial to do this properly.
Test Plan: Eyeball it.
Reviewers: Blessed Reviewers, epriestley
Reviewed By: Blessed Reviewers, epriestley
Subscribers: epriestley, Korvin
Differential Revision: https://secure.phabricator.com/D13422