Split the XInput and DirectInput code so Windows RT can use the existing XInput support.

--HG--
rename : src/audio/directsound/directx.h => src/core/windows/SDL_directx.h
rename : src/haptic/windows/SDL_syshaptic.c => src/haptic/windows/SDL_windowshaptic.c
rename : src/haptic/windows/SDL_syshaptic_c.h => src/haptic/windows/SDL_windowshaptic_c.h
rename : src/joystick/windows/SDL_dxjoystick.c => src/joystick/windows/SDL_dinputjoystick.c
rename : src/joystick/windows/SDL_dxjoystick_c.h => src/joystick/windows/SDL_dinputjoystick_c.h
rename : src/joystick/windows/SDL_dxjoystick_c.h => src/joystick/windows/SDL_windowsjoystick_c.h