Simplify code
Use new style classes
Improve constant definitions
Optimize __call__
Improve __getitem__
Improve __setitem__
Optimize __delitem__
Improve __iter__ code
Improve __contains__
Reorganize TODO
Improve code
Improve code
Code improvements
Use a constant for the base dictionary (allow easy customization)
Improve code
Add idea to TODO
White space fixes
Simplify code
Add idea to TODO
Change the structure of the tree object