Bump deps to build on modern toolchain.

Update README with fixed performance.

Use BVH in same places as C++ for fairness.

Scale combinator.

Add unnecessary Cargo.lock change from 1.34 upgrade

Cleanups.

Update README.

Update book 2 render with higher quality image.

Formally ban unsafe code.

Remove unused parameter from BVH.

Implement Object for Box<dyn Object>

Fix some differences from the book algorithm.

Assorted cleanups after sprint.

Implement final scene from second book.

Make concrete Object impls Clone.