Perform robustness testing with Hypothesis

[gkapfham]

While GatorGrader currently has a high coverage test suite, it is good idea for us to perform additional testing, perhaps by using a tool like Hypothesis to generate random input values. These tests could be marked separately and, perhaps, not during during the Travis CI build. However, this new type of testing could be useful for finding hard-to-discover bugs in "corner cases" of, for instance, parameter verification.