Sorted dict 1

Pull request for SortedDict and BalancedTree23 taking into account Kevin Squire's feedback from the past 12 days.
Stephen, thanks for the pointer to that conversation (which is [here](https://groups.google.com/forum/#!topic/julia-users/F_ncyfP2vxg)).  You are absolutely right, and I hadn't realized that about tuples!  So definitely ignore this suggestion.

At this point, I've gone through the code well enough that I think I have a good feel for it, and I don't have any further comments at this time.  Whenever you can, feel free to push further changes to this branch, and post back here so I can take a look.  (Just FYI, I'll be out and have little or no computer access from Oct 3-12.)