Sorted dict 1

Pull request for SortedDict and BalancedTree23 taking into account Kevin Squire's feedback from the past 12 days.
I agree that that is a lot of iterators, but generally, that is what I was thinking.  Does this work for you?

(I'm on vacation right now, and only have very limited internet, so my responses will probably be shorter and less frequent than usual (if that's possible).  Sorry about that!)