Sorted dict 1

Pull request for SortedDict and BalancedTree23 taking into account Kevin Squire's feedback from the past 12 days.
Could be written as
```julia
KDRec(p::Int, k1:K, d1:D) = new(p,k1,d1)
```
Especially for cases like this, where the one-liner version is very short, this is preferable.  

cf: https://github.com/JuliaLang/julia/blob/master/base/dict.jl#L247, https://github.com/JuliaLang/julia/blob/master/base/dict.jl#L724