INT 21 - DOS 2+ - "CLOSE" - CLOSE FILE
        AH = 3Eh
        BX = file handle
Return: CF clear if successful
            AX destroyed
        CF set on error
            AX = error code (06h) (see AH=59h)
Note:   if the file was written to, any pending disk writes are performed, the
          time and date stamps are set to the current time, and the directory
          entry is updated
SeeAlso: AH=3Ch,AH=3Dh,INT 2F/AX=1106h,INT 2F/AX=1227h