Sorted dict 1

Pull request for SortedDict and BalancedTree23 taking into account Kevin Squire's feedback from the past 12 days.
Kevin,

Please keep the comments coming!  For this particular comment, I have a 
question for you.  Steven Johnson commented in June that tuples are not 
meant to be stored inside of large arrays.  I don't know exactly how to 
give you the URL of his comment, but you should be able to find it in a 
thread that I started on the Julia users' group if you google:

julia users group vavasis question immutable and arrays

Has this changed since June?  In my other big Julia code, I am storing 
(x,y,z) coordinates using the ImmutableArray package, but tuples would be 
easier if they are suitable for this purpose.

-- Steve



On Tue, 23 Sep 2014, Kevin Squire wrote:

> 
> In src/balancedTree.jl:
> 
> > +##     These are the three children node numbers.
> > +##     If the node is a 2-node (rather than 3), then child3 == 0.
> > +##     If this is a leaf then child1,child2,child3 are subscripts
> > +##       of data nodes, else they are subscripts  of other tree nodes.
> > +## splitkey1:
> > +##    the minimum key of the subtree at child2.  If this is a leaf
> > +##    then it is the key of child2.
> > +## splitkey2: 
> > +##    if child3 > 0 then splitkey2 is the minimum key of the subtree at child3.
> > +##    If this is a leaf, then it is the key of child3.
> > +## Again, there are two constructors for the same reason mentioned above.
> > +
> > +immutable TreeNode{K}
> > +    child1::Int
> > +    child2::Int
> > +    child3::Int
> 
> Since TreeNodes are immutable, it would be worth exploring changing child1, child2, and child3 to a three tuple of
> type (Int,Int,Int).
> 
> immutable TreeNode{K}
>     child::(Int,Int,Int)
>     parent::Int
> 
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