Add Haskell checkers

Add syntax checkers using hdevtools, ghc and hlint.  The former two
perform syntax checking and are chained to hlint which provides style
checking.
Fix Haskell provisioning
Fix hdevtools pattern
Update the changelog
[Fix #32, #162] Merge branch 'purcell-haskell'

* purcell-haskell:
  Update the changelog
  Fix hdevtools pattern
  Fix Haskell provisioning
  Add Haskell checkers
Mention command names in changelog
Force-install all necessary Python tools