Added simple AOV example. Added support for light categories as part of shrimp generated output vars, together with __nondiffuse, __nonspecular, __inShadowC. Added support for light categories in the shading functions blocks. All illuminance() statements now have a respective category variable. Updated the examples to use light categories. Updated all light blocks so that the user can set the light category. The grid shader now outputs correctly to aov_surface and aov_diffuse AOVs, and the default distant light shader now has __nondiffuse and __nonspecular.
