AdditiveGroup instances for Angle types
Remove Angle constraint on Spherical type

avoid Datatype Context
New Camera type & CameraLens class; perspective & orthographic instances
Add types PointLight, ParallelLight

PointLight represents a spherically symmetric light source
ParallelLight represents parallel light rays covering the entire scene
Export Camera and Light modules
Directions do not form an AdditiveGroup
Merge pull request #114 from diagrams/threeD-render

Three d render