INT E0 - PCROBOTS v1.41 - "INVISIBILITY" - CONTROL ROBOT'S INVISIBILITY DEVICE

	AX = 0022h
	BX = new state (0000h become visible, 0001h become invisible)
Return: nothing
Notes:	this function has no effect if the robot is not capable of invisibility
	the robot can only stay invisible for 100 turns, after which it will
	  automatically become visible; it must also be remain visible for
	  as many turns as it was invisible before it can turn invisible
	  again
SeeAlso: AX=0024h,AX=0080h