Proposal: Data.Functor.<.> for `fmap f2 . f1`

[Ömer Sinan Ağacan]

I don't know if "I find this very useful" is enough for adding a function to
base, but here it goes:

    infixl 4 <.>
    (<.>) :: Functor f => (b -> c) -> (a -> f b) -> (a -> f c)
    f1 <.> f2 = fmap f1 . f2
    {-# INLINE (<.>) #-}

I first defined this couple of months ago and I find myself looking for this
function all the time now.

One problem with this is that the name is used by widely used `filepath`
library.