Allow to use ps4 controller wirelessly

- use `pysdl2` instead of `pygame` (thanks @ak1394)
- update documentation
- remove native support of joystick as it seems to be dropped

I test it with my ps4 controller on Mac OSX 10.9.

I think it **requires** to be tested with other controllers and systems (linux & windows).

I could test on linux, with my ps4 controller and my awful BigBen controller.