Add initial scaffolding

Also add .gitignore file.

Feature-Start: initial-scene
Add initial version of IndependentSampler

Also add randFloat32() function and use it instead of
math.rand.Rand.Float32(), which is buggy.
Add scaffolding for RadianceMeter
Flesh out Spectrum and RadianceMeter
Add scaffolding for Ray
Add scaffolding for PathTracer.SampleSensorPath()
Add PrimitiveList
Add GeometricPrimitive and more scaffolding
Add Sphere and more scaffolding
Flesh out Ray
Add Diffuse material
Use hollow sphere test scene

Feature-End: initial-scene
Implement cosine-weighted hemisphere sampling

Feature: cosine-weighting
Build the renderer from a config map

Feature-Start: read-config
Build the scene from a config map

Also add comments about hollow sphere scene.
Read config from file
Process any number of config files on the command line

Feature-End: read-config
Communicate sensor extent to renderer

Feature-Start: multiple-sensors
Make sensors part of the scene

Add GetSensors() function to Primitive.

Add PointPrimitive.

Add "black" Spectrum type.
Add hollow sphere with center light example

Feature-End: multiple-sensors