Dead zone compensation

This branch changes how the deadzone is handled. Before it was impossible to activate any range of the joystick that was inside the deadzone, which made it completely impossible to sneak in Banjo Tooie, or was slowly in any other game.

I also decreased the size of the deadzone (since the original 1/4th of the range felt like way too large of a deadzone) to 0x1000 which is now 1/8th of the range. (This should ideally be a Core Option in libretro). If I figure this out I'll send another pull request on another fork.