New RGBPromotion example scene, do expose, document renderer RGB promotion algorithms.  Incomplete.
New RGBPromotion example scene, do expose, document renderer RGB promotion algorithms.  Incomplete.

RenderToolbox3/RenderToolbox3,tlian7/RenderToolbox3,RenderToolbox3/RenderToolbox3,RenderToolbox3/RenderToolbox3,tlian7/RenderToolbox3,RenderToolbox3/RenderToolbox3,tlian7/RenderToolbox3,tlian7/RenderToolbox3