Added MultiMap[F, K, V].sliding(Int): F[MultiMap[F, K, V]]
Added MultiMap[F, K, V].flatMapValues(V => G[W]): MultiMap[G, K, W]

This generalizes the previous MM.flatMapValues by now allowing the container type to change.
Implemented by copying Unapply from scalaz.
Merge branch 'master' into 2.9

Conflicts:
	core/src/main/scala/pimpathon/multimap.scala