Add hdevtools linter for haskell

This adds support for the hdevtools haskell linter
https://github.com/hdevtools/hdevtools

The output for hdevtools is near identical to the ghc output so this
also extracts the ghc handler into the handle file and adds tests

ale_linters/haskell/hdevtools.vim

@@ -0,0 +1,9 @@
+" Author: w0rp <devw0rp@gmail.com>
+" Description: hdevtools for Haskell files
+
+call ale#linter#Define('haskell', {
+\   'name': 'hdevtools',
+\   'executable': 'hdevtools',
+\   'command': 'hdevtools check -g -Wall -p %s %t',
+\   'callback': 'ale#handlers#HandleGhcFormat',
+\})