Proposal: Add conspicuously missing Functor instances for tuples

[Henning Thielemann]

On Thu, 18 Feb 2016, Edward Kmett wrote:

> Traversable's sequence gives you canonical distributive law for this functor. 
> 
> sequence :: (e, f a) -> f (e, a)

I have my own functions Func.mapFst, Func.mapSnd. This seems to better 
reflect the symmetry of the pair members. They only need (Functor f), not 
(Applicative f) like 'sequence' does.
   http://code.haskell.org/~thielema/utility/src/Control/Functor/HT.hs