AAS - Ascii Adjust for Subtraction

	Usage:	AAS
	Modifies flags: AF CF (OF,PF,SF,ZF undefined)


	Corrects result of a previous unpacked decimal subtraction in AL.
	High order nibble is zeroed.


				 Clocks			Size
	Operands	 808x  286   386   486		Bytes

	none		  8	3     4	    3		  1


	- see Instruction Timing