Untested CoflatMap laws

[ceedubs]

There are several laws defined in CoflatMapLaws that aren't checked in CoflatMapTests. It looks like they require some additional Eq instances, but other than that I'm not sure whether or not there is a good reason they aren't currently included. Does anyone know?

Paging @fthomas and @non due to git history :)

[fthomas]

That is the associativity law of coflatMap expressed in terms of Cokleisli composition. There is also a law that shows the associativity of Kleisli composition in FlatMapLaws. I've added them because the associativity is more apparent in this formulation (see also this Gitter discussion).

Since those laws are more or less duplicates of existing laws, I'd just test them with a single type so that code coverage do not mark them as unused. If they pass for one type, I guess the other tests and laws guarantee that they also pass for all other types.

I'll try to come up with test for those.