Split up monolithic modules

Fixes #62.

So far this is about four seconds slower than master. I think that's acceptable. I timed a build with these commands:

``` sh
$ time \
  ruby library/Strive/Lenses/classes.rb > library/Strive/Lenses/Classes.hs &&
  ruby library/Strive/Lenses/instances.rb > library/Strive/Lenses/Instances.hs && 
  make format all
```