INT B3 - ZIPKEY - LOOK UP ZIPCODES FOR A GIVEN CITY
        AH = 79h
        BL = ZIPKEY state code of first state to search
        DS:SI -> city name, terminated with 0Dh if complete name, 00h if prefix
Return: AL = ZIPKEY state code of first matching state
        BH = number of matching entries (set to 51 if more than 50)
        DX = zipcode region of first match (0-999)
        CL = last two digits of first zipcode in first range (0-99)
        CH = last two digits of last zipcode in first range (0-99)
Note:   to find all matching cities, repeat search with BL set to one more than
          the returned AL
SeeAlso: AH=7Ah