MSC: int _bios_keybrd( int cmd )

	- prototype in bios.h

	- cmd	= _KEYBRD_READ	return next keystroke w/o echo (INT 16,0)
		= _KEYBRD_READY	test if key avail; 0=none  (INT 16,1)
		= _KEYBRD_SHIFTSTATUS  return shift key status (INT 16,2)
		= _NKEYBRD_READ	return next keystroke w/o echo (INT 16,10)
		= _NKEYBRD_READY	test if key avail; 0=none  (INT 16,11)
		= _NKEYBRD_SHIFTSTATUS return shift key status (INT 16,12)

	- AND returned value with 0x00FF to get ASCII value
	- _NKEYBRD_READ, _NKEYBRD_READY, _NKEYBRD_SHIFTSTATUS are available
	  on AT and newer machines only
	- Turbo C uses bioskey()
	- see  INT 16