Add 3D raytrace visualizer

[sethrj]

Add a multi-geometry 3D raytracer for validation/code comparison

C++ back end:

• [x] Add color and PNG export
• [ ] Rename Raytracer to Rasterizer or Linetracer
• [ ] Add camera point (and background color?) to image input
• [ ] Add color state
• [ ] Implement rasterizer on a 2D grid of states (one thread per pixel?) or maybe just trace sequentially over the lines

Future work:

• [ ] Translucent volumes and color mixing
• [ ] Material processing