[Bf-python] Modified RenderEngine API Proposal

[Tom M]

A few minor comments

1) interactive rendering context

a usage scenerio that is possible with Bodypaint is that the renderer
is only rerendering where the paint stroke is occurring while the
stroke is happening.  Right now context doesn't seem like we can
provide this information to the renderer of what areas were changed
since last render.

2) for faster rendering of animations some renderers need knowledge of
the previous and next frame since that can change the sampling
strategy to exploit temporal and spatial coherence of frames.

ACCELERATED RAY TRACED ANIMATIONS EXPLOITING TEMPORAL COHERENCE
http://contentdm.lib.byu.edu/ETD/image/etd915.pdf

LetterRip