Stag hunt and snow drift functions

I've whipped up stag hunt and snow drift functions that are just copy and pasted from the prisoner's dilemma functions. It might save you some time tomorrow. 

The only file you should consider merging is simulation.coffee.md - the other modifications are relics of my tinkering with the web page. I hacked together a basic list of the player colours that displays down the left side of the page so that I could keep track of the various strategies.