INT B3 - ZIPKEY - GET NAME OF PRIMARY CITY FOR A ZIPCODE REGION                 
	AH = 7Eh
	DX = zipcode region (0-999)
	ES:DI -> buffer for name
Return: CF set on error
	    AL = FFh region does not exist
	CF clear if successful
	    AL = ZIPKEY state code
	    ES:DI points one byte beyond end of name
SeeAlso: AH=76h