Be more specific about camera attribute names
Re-converge some diverged bits of simplerend in testshade vs testrender.
In particular, microfacet closures, named transforms, and camera parameters
now work the same way in both.
Allow getattribute of camera attribs for testrender & testshade
and make a test for it.
Merge pull request #393 from lgritz/lg-camera

Camera attributes: document, exemplify, test