Found issue in rb-tree test. Fixed. Tests fail.

The problem was that the black node balance validation function was
never incrementing the black node count. The count was always 0 and so
was always balanced. Fix this defect. Now it is apparent that the black
nodes are unbalanced and the red-black tree is broken.

Next step is to fix the tree.
Adding Seed(...) function for OrderMaker

This allows us to for the random number generator into a known state so
we can more easily reproduce failing tests.
Moved tree validation into tree.go

This is intended to make way for different implementations of RB-trees
Fixed defect in deletion

Now correctly colouring rotations for the case where a black sibling has
red children. Previously we weren't recolouring afte the rotation at
all.

This does not fix all of the defects.
Bottom up Red-Black tree implementation.

Passes all tests.