Reorganize module namespace

- Remove Language.Haskell prefix from all modules
- Move 'GHCMod.*' to 'GhcMod.Exe'
- Move 'GhcModExe' to 'GhcMod.Exe'

test/CabalHelperSpec.hs

@@ -4,9 +4,9 @@ module CabalHelperSpec where
 import Control.Arrow
 import Control.Applicative
 import Distribution.Helper
-import Language.Haskell.GhcMod.CabalHelper
-import Language.Haskell.GhcMod.PathsAndFiles
-import Language.Haskell.GhcMod.Error
+import GhcMod.CabalHelper
+import GhcMod.PathsAndFiles
+import GhcMod.Error
 import Test.Hspec
 import System.Directory
 import System.FilePath