rename file.
add monad law "proofs"
remove composable extension that isn't needed.
remove superfluous specs.
remove specs that are covered by "proofs"
move high level specs to maybe spec.
Merge pull request #14 from unsymbol/feature/prove-maybe-is-a-monad

Prove maybe is a monad

closes https://github.com/unsymbol/ribimaybe/issues/11