INT 15 - MultiDOS Plus - MAP SEMAPHORE NAME TO NUMBER
        AH = 1Ah
        DS:SI -> 8-byte name
Return: AL = status
            00h successful
                AH = semaphore number (20h-3Fh)
            04h out of string space
Notes:  all eight bytes of the name are significant
        if the name does not already exist, it is added to the name table and
          associated with a free semaphore number
        names cannot be destroyed
SeeAlso: AH=1Ch"MultiDOS",AH=1Dh"MultiDOS"