Create a persistent `BitSet` data structure

`BitSet` is extremely useful when you want to test the presence of some enumerable entity, i.e. a compact `Set` of `Booleans`.
We might want a pure one in Javaslang also.

It could be based on [Scala](https://github.com/scala/scala/blob/2.12.x/src/library/scala/collection/immutable/BitSet.scala)'s or  [Haskell](http://hackage.haskell.org/package/bitset)'s implementations.
