Implement test cases for correlated equilibria

[tturocy]

There is a branch correq which contains a preliminary implementation of computing the set of correlated equilibrium payoffs for two-person games.

Some test cases should be written for this, including exercising the contains method for the object representing the set of payoffs.

[rawls238]

@tturocy, going to try to tackle this unless it's already been resolved

[tturocy]

Please feel free to have a go!