adding thread to handle inputs and introduce a delay

modified:   SnakeGame.hs
	modified: getInputs
		now read on the standard input and modify a MVar
	modified: readInputs
		now handle the Esc key to quit
	modified: updatePosition
		in the case of Unknown input the snake now moves in
		the previous direction

modified:   main.hs
	introduction of threads and the resulting inputs handling