[Bf-python] hints for optimizing python exporters, using Blender2Radiance for eg.

[Francesco Anselmo]

Hi Cam,

I really appreciate your very detailed explanations about how
to optimise my (or any) exporter code. As you may imagine, I've not
paid very much attention to fine tune the code to run it quicker,
just did it the dirty way to have a good Radiance model in the end
(at least good for my work).

I'll keep your precious hints in mind when I'll work again on the b/rad
code, maybe later this year since I'm quite busy at work. My TODO list
is even longer, now! ;)

Thanks, Cam!

Francesco