* Add stack-build linter for Haskell
The stack-build linter works better than the other two linters when
you're working with an entire Haskell project. It builds the project
entirely and reports any errors.
The other two Haskell GHC linters only work on single files, which can
result in spurious errors (for example, not being able to find imports).
* Document all available Haskell linters
* Split GHC checkers into separate files
