Allow custom settings to be passed through genetic simulations.

[HyperCodec]

With some APIs like neat, the object implementing crossover/division/randomlymutable would need to access some settings. Right now, the only ways to do that are:

1. have every agent contain a settings object, which uses extra memory (this is what neat does)
2. use statics for global settings (statics are bad and should be avoided at all costs)

Ideally, we would want to add another generic field to GeneticSim or something that bubbles down an arbitrary, simulation-wide (immutable) setting value to all division/crossover/randomlymutable methods.

[HyperCodec]

This should be much easier with the the new APIs being implemented in #96. However, maybe this issue should remain open, as reproduction methods only accept rate as a parameter, but not any custom types.