Implements feedback from #11. Specifically:
1. LOr and ROr move to `Or.LeftOr` and `Or.RightOr`.
2. Constructors are still public, but `left` and `right` preserved in
`OrFunctions` to infer `Or`. Use what you like.
3. Only the Scaladoc is ripped from Scalaz.
Also tries to adhere to the emerging consensus on #27.
Preliminar benchmarking showed monomorphism is faster than polymorphism,
and that implementing other operations using fold/bimap is immeasurable.
The second finding is dubious with respect to allocations. If someone
can prove these guilty via benchmark, we can revisit.
I'd like to add tests after #29 happens.