Integrate menu with play/exit options.

Add:
	src/menu.c, src/menu.h
		-govern the menu. Called in src/termcrate.c main(), and
		currently allow user to begin playing/exit the game.

	makefile
		-necessary compilation statements for audio.c/menu.c

	src/graphics.c
		-add render functions for menu()

	src/graphics.h
		-add colors for menu buttons/selected buttons.