Renderer 2, now with 100% less threading tools

I've rewritten the renderer to see if I can make a better model the
second time around. I was having a rough time untangling parts and
refactoring it piece-by-piece.

Next is to hook up the new rendering parts into a single-threaded
build. Once the parts work again, I can look into thread pooling
machinery.

src/scene.rs

@@ -169,7 +169,6 @@ pub fn degrees_to_radians(degrees: f32) -> f32 {
     degrees * std::f32::consts::PI / 180.0
 }
 
-#[derive (Clone, Copy)]
 pub struct Camera {
     origin: Vec3,
     lower_left_corner: Vec3,