Adds support for Xbox and Nintendo style game controllers. The gamepad
controls are documented on the README and in the game's Settings window.
The buttons are not customizable yet, except that the player can choose
between two button styles:
* X Style (default): "A" button is on the bottom and "B" on the right.
* N Style: swaps the A/B and the X/Y buttons to use a Nintendo-style
layout instead of an Xbox-style.
Noah Petherbridge
4de0126b19
