Breed diverse parents

[blexim]

Observation: if we have 10 test vectors, and programs A and B, if A passes tests 1,3, 5 and B passes tests 2, 7, 8 we might want to breed them together. If C passes 1, 3, 5, 7 it's fitter than B but is unlikely to make a better mate for A than B is.

Think about having a fitness function output a vector of fitness values for each test case, then breed together solutions that score well on different tests.