INT 21 - European MSDOS 4.0 - SLEEP
        AH = 89h
        CX = time in milliseconds or 0000h to give up time slice
Return: CF clear if successful
            CX = 0000h
        CF set on error
            AX = error code (interrupted system call)
            CX = sleep time remaining
Desc:   suspend the calling process for the specified duration
Notes:  the sleep interval is rounded up to the next higher increment of the
          scheduler clock, and may be extended further if other processes are
          running
        this call may be interrupted by signals (see AH=8Dh)
        reportedly called by Microsoft C 4.0 startup code
        background processes have higher priority than the foreground process,
          and should thus periodically yield the CPU
SeeAlso: INT 15/AX=1000h,INT 2F/AX=1680h,INT 7A/BX=000Ah