[Browse] Option to show symbol parents

E.g. Nothing is a constructor of Maybe, so it has
parent Maybe.

This is useful for completion, e.g. with `(..)` imports

src/GHCMod/Options/Commands.hs

@@ -255,6 +255,10 @@ browseArgSpec = CmdBrowse
             $$  long "detailed"
             <=> short 'd'
             <=> help "Print symbols with accompanying signature"
+        <*> switch
+            $$  long "parents"
+            <=> short 'p'
+            <=> help "Print symbols parents"
         <*> switch
             $$  long "qualified"
             <=> short 'q'