Add flipped fmap

Hello, I would like to propose adding a flipped variant of <$> to Data.Functor: (<$$>) ∷ Functor f ⇒ f α → (α → β) → f β (<$$>) = flip (<$>) Please see the ticket for motivation and patch: http://hackage.haskell.org/trac/ghc/ticket/3962 Discussion period: 2 weeks. regards, Bas