INT 10H 101bH: Convert DAC Colors to Gray-Scale Values

                                                          Compatibility: VGA
 Expects: AX    101bH
          BX    first color register to convert
          CX    number of color registers to convert
 Returns: (none)
    Info: This converts (sums) a range of DAC color values into gray-scale

          The R,G,B of each of the specified registers is weighed according
          to a BIOS internal system and replaced with values that are
          displayed as shades of gray.

   Notes: ž In performing the conversion, the BIOS uses:
              30% of the Red value
              59% of the Green value
              11% of the Blue value

          ž The BIOS performs gray-scale summing by default when it detects
            a monochrome display.  That data may be found in the rMiscFlags
            field of the VgaDynamicStateRec.

See Also: INT 10H 10H: EGA/VGA Palette Functions
          INT 10H: Video Services
          EGA/VGA Data Areas