Added evolution code.
Fixed typo in darwin::evolve and darwin::selection::roulette
Split darwin/mod.rs into seperate files
Split Genome into Genome: Crossover + Mutate
Made fields in neural::{Layer,Network} public.
Implemented some neuron crossover code.
Made Crossover::crossover return two offspring
Implemented neural network crossover.
Added values(), get_values() and set_values() to Network
Got mutations working
Added preliminary evolution support to simulation.