Make findAllele returns int instead of integer
Add tests for a few new methods in Genotype classes
Add cache for GenotypeValidator
Update FitnessEvaluator cache to use Genotype as key instead of string
Add hashCode override for Genotype

Uses String hashcode.
Use HashMap for cache to store both valid and invalid genotypes
Change interface for crossover to use ENUM for offspring SINGLE/PAIR
Add implementation of PMX
Add test for PMX and Recombinator