Added sdl events, keypad structure, intregrated sdl with main code

        modified:   Makefile
	modified:   debugger.c
	modified:   dmg.c
	modified:   dmg.h
	modified:   main.c
	new file:   main.h
	modified:   memory.c
	modified:   memory.h
	modified:   screen.c
	modified:   screen.h
	modified:   sdl.c
	modified:   sdl.h
	new file:   sound.c