Reorganize module namespace

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

test/CradleSpec.hs

@@ -2,8 +2,8 @@ module CradleSpec where
 
 import Control.Applicative
 import Data.List (isSuffixOf)
-import Language.Haskell.GhcMod.Cradle
-import Language.Haskell.GhcMod.Types
+import GhcMod.Cradle
+import GhcMod.Types
 import System.Directory (canonicalizePath)
 import System.FilePath (pathSeparator)
 import Test.Hspec