Clarify relationship between Functor and Applicative

[roconnor at theorem.ca]

In the applicative documentation, it says for an Applicative functor f:

The Functor instance should satisfy

       fmap f x = pure f <*> x

I think the documentation should be clarified that this does not need to 
be checked because it is a consequence of the other applicative laws.

See <http://hpaste.org/44315/applicative_implies_functor>.

-- 
Russell O'Connor                                      <http://r6.ca/>
``All talk about `theft,''' the general counsel of the American Graphophone
Company wrote, ``is the merest claptrap, for there exists no property in
ideas musical, literary or artistic, except as defined by statute.''