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.
Because I was already using the format for the returned value, but you're right it's better to just have the constant in the string.