Revised optimizer and its tests; issue #30

@subutai @scottpurdy please review.
The revisions to optimizer.py are to included bounded optimization.
optimizer_test.py was redone to test against more cases (parameter boundaries, local vs global max) and correct some calculations. I also added detailed failure messages.
You get the same effect with `import nab.optimizer.twiddle as optimizer` with fewer lines of code and no extra member variables.