Use gpio-keys driver for EV3 keypad

Here is an idea. We can use the existing gpio-keys driver in linux to bind the EV3 buttons as if they are keyboard keys. It shows up in /dev/input/eventX just like any other input device. I think this would make programming for the keys much easier that using a custom driver as most languages have existing libraries for standard keyboard input. The buttons are mapped to UP, DOWN, LEFT, RIGHT, ENTER and ESC.