Feature compound lens #15

[jackfirth]

Closes #15 and #84 and creates an unstable/lens module for more additions

[AlexKnauth]

Is compound-list-lens the best name for this? The word compound makes me think of nested lenses produced by lens-compose or lens-thrush.

Would something like mapped-list-lens be a better name, or?

[jackfirth]

I generally think of compound lenses as any lens created by combining two or more other lenses, but it may be good to describe the difference between combining lenses in series (compose and thrush) vs in parallel (compound list and hash)

[jackfirth]

Or an entire subcollection lens/compound that contains compose, thrush, and this combinator