Removed AbstractEntry as it was only implemented by
SubSetLimitedMapEntry. Moved JavaDoc and Map.Entry compliant
hashCode/equals to the latter.
Add bound() method to IndexSet as documentation and updated the rest of
the documentation.
Documented IndexFunction interface
Added PowerOfTwo util for operations surrounding powers of two. These
are used by the hash index functions and consorts.
More documentation for HashFunction
Moved DefaultIndexedUniverseIterator to only package where it's been
used, made it package private and renamed it to IndexedUniverseIterator.
Some more documentation