Changed the official artwork to the work by cramer. Added random pipe height.
	modified:   Makefile
	deleted:    builds/a.exe
	new file:   builds/openFLAP.exe
	modified:   ground_pipes.c
	modified:   main.c
	modified:   move_bird.c
	renamed:    resources/background.png -> resources/background-old.png
	renamed:    resources/background-2.png -> resources/background.png
	renamed:    resources/ground.png -> resources/ground-old.png
	renamed:    resources/ground-2.png -> resources/ground.png
	renamed:    resources/pipes.png -> resources/pipes-old.png
	renamed:    resources/pipes-2.png -> resources/pipes.png