improved definition of pointed functor

[jethrolarson]

After reading https://stackoverflow.com/questions/39179830/how-to-use-pointed-functor-properly I thought we should make the definition less wrong.

[jethrolarson]

I think when I wrote the original I was looking at the "Pointed" typeclass in haskell which doesn't have a requirement of functor so I didn't think that it was necessary. And in a way it's not. A type is pointed if any value can be lifted into it but intuitively a type is only a pointed functor if it's both pointed and a functor.