Instances for ReaderT and MaybeT?

[Zemyla]

Because ReaderT e is pretty much Compose ((->) e), there should be derived Semialign, Zip, Repeat, and Unzip instances for it. Also, even though Compose ((->) e) doesn't have an Align instance, nil = ReaderT (const nil) should be law-abiding.

Additionally, MaybeT m is isomorphic to Compose m Maybe, so it also would get Semialign, Align, Zip, Repeat, and Unzip instances. There might also be a possible law-abiding Unalign instance, but I'm not sure right this moment.

[phadej]

PRs are welcome

EDIT: "should" should be witnessed. It's not obvious to me that const nil would or wouldn't work.