The keyboard API allows me to bind multiple buttons to the direction
keys, unlike the controller API. I probably need to rethink the
controller API at some point.
With this backend, CSE2 can run on the Wii U.
It's not ideal - it doesn't have its own renderer yet, so it just
uses the software renderer, and it only displays on the gamepad,
because drawing to the TV as well makes the game lag.
Also there's no sound.
Also the lack of input rebinding is annoying.
