Deprecate mapsExposed and mapsMExposed

[treeowl]

I don't believe that either mapsExposed or mapsMExposed actually exposes anything it shouldn't. Whereas hoist must be passed a monad morphism to get sensible results, I'm pretty sure these functions will work with arbitrary natural transformations.

[andrewthad]

This is no longer the official repo for streaming. Please continue discussion of this issue here.