Summary:
This adds a lint engine for `hlint`, which is the standard and most general Haskell lint tool around these days.
Signed-off-by: Austin Seipp <aseipp@pobox.com>
Test Plan: Install `hlint`, and run `arc unit`.
Reviewers: #blessed_reviewers, epriestley
Reviewed By: #blessed_reviewers, epriestley
Subscribers: epriestley, Korvin
Projects: #arcanist
Differential Revision: https://secure.phabricator.com/D10250
