INT 33,5 - Get Mouse Button Press Information

	AX = 5
	BX = 0	left button
	     1	right button


	on return:
	BX = count of button presses (0-32767), set to zero after call
	CX = horizontal position at last press
	DX = vertical position at last press
	AX = status:

		|F-8|7|6|5|4|3|2|1|0|  Button Status
		  |  | | | | | | | `---- left button (1 = pressed)
		  |  | | | | | | `----- right button (1 = pressed)
		  `------------------- unused