Adding an ignore function to Control.Monad

[Isaac Dupree]

Gwern Branwen wrote:
> ## Control.Monad.ignore :: m a -> m ()
> - Isaac Dupree

(for the record, I wanted to generalize it to Functor, maybe you're 
counting from early in the discussion before that was brought up :-)

> I think consensus has been reached to:
> 1) add X
> 2) add X :: f a -> ()
> 
> The exact name - whether ignore/void/discard - is not so clear with
> consensus. So I'm just going to name it 'void' for consistency with
> Foreign and foreign languages.

yay!

-Isaac