[lint] Add HLint-based Haskell linter

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