Add sample players
Create README.md
Start extracting species into a separate concept

I'm going to extract common parameters of creatures into a table describing the
whole species. Otherwise there's too much argument passing.
Give less energy from photosyntesis

It was stupid that grass had to prevent its own growth to limit its numbers.
I've changed photosynthesis to give less energy the more plants there are in the
area... this is supposed to simulate how plants compete for light. Probably in
the future it will make sense to give some benefits to bigger plants.

As a plus, this change allowed me to simplify algorithm of grass. Minus is a
significant performance drop.
Sort creature_look result to keep it deterministic

Creature_look was returning creatures in an arbitrary order, resulting in an
indeterminism and preventing repeatable simulations.

Fixed by sorting the creatures before returning them to the player's code.
Optimize counting plants
Add tournament script
Add option to skip drawing