Sorted dict 1

Pull request for SortedDict and BalancedTree23 taking into account Kevin Squire's feedback from the past 12 days.
> Just for your information, I am planning to carry out this suggestion with
one small change: in the definition of Token, T will not be declared a
subtype of Associative.  The reason is that I also need tokens for
MultiMap and SortedSet, which are not subtypes of Associative.

Sure, that makes sense.