Organized animal eating, etc. properly.

Added species class that works like a base. Vector of species used to set up animals. Initializing new animals not implemented yet.
Added structure that controls animal's eating/behavior. Animal class has a functor that specifies how it will act. Herbivore/carnivore, and later will add individual/herd for behavior. For now there's just a filler.
Herbivores can eat just grass or berries. Animals can be different sizes. Carnivores act similarly to herbivores, but search for meat food instead. Will add omnivores later.