Support writing the mastering display color volume SEI message

Use --mastering-display to specify the properties of the reference display.
A formatted string with all 10 values is required: G,B,R primaries and
white point coordinates, plus max/min brightness. Coordinates are in
0.00002 increments. Brightness units are 0.0001 cd/m^2.

For example, a 1000 nit BT.2020 display with a 0.0001 nit black level:
--mastering-display G(13250,34500)B(7500,3000)R(34000,16000)WP(15635,16450)L(10000000,1)