Initial commit of Java implementation, generified.  (Haven't gotten to
the CachedHash files yet, though.)
Various small changes and cleanups:

() 'PureTreeList.with' now appends if the index is equal to the size.

() The abstract classes no longer implement Cloneable (pointlessly and
confusedly).

() The implementations classes now have a static 'eql' method that
implements the Java equality idiom, and they call it when appropriate.

() 'PureSet.arb' now throws 'NoSuchElementException' on an empty set.
Bringing back a couple of minor changes from the GitHub tree.
Removing Java implementation from main FSet repo.
Tweak the interface of RANK, and export it and AT-RANK.  (WARNING:
these are only lightly tested.)
Merge branch 'master' of github.com:slburson/fset