New class that allows tabu search functionality to be added to pre-existing optimizers.

Add the class TabuOptimizer to optimizer.py, as well as two example subclasses, and doctests.  TabuOptimizer overwrites BlackBoxOptimizer's _oneEvaluation method allowing (most) of the functionality described in http://www.cse.unt.edu/~garlick/teaching/4310/assign/TS%20-%20Tutorial.pdf to be added to any BlackBoxOptimizer with little additional code or computational load.