Added controller support

I realised that it would be super easy to add USB game controller support; so I added it. I can't promise the controls are 100% predictable, since I only have off-brand game controllers to test with, but it should be easy enough to figure it out.

Perhaps, in time, I'll be able to narrow down what the control differences are. Perhaps I'll shell out for an xbox controller, a ps4 controller, a switch pro controller. Perhaps I'll add those to a help menu.

TIME WILL TELL!