Luminosity difference from 1% to 2% is much greater than 99% to 100% about fade9685 HOT 3 OPEN

Added a Rec709 adjustment function and command line argument to enable it. The argument is unused pending test with hardware (no hardware onsite at the moment)
b506659

from fade9685.

As added it won't work correctly. Will need to work out a different method for the step value in the fade loop.

Note: Not currently enabled.

from fade9685.

Thinking about this more, and I think it should work fine without messing with the step value. The fade rate might still be a wee bit odd, but when changing from 95% to 100% you would actually see a difference, and 1% to 2% would not be such an alarming difference.

Need to test.

from fade9685.