Book 1 content - optimized and cleaned up

Covers Peter Shirley's Book 1 - Raytracing in one week-end
Multithreaded, reasonably optimized (5.5% faster than GCC)
Cleaned up the module

Initial RayTracingInOneWeekend implementation

Finish adapting the content of this book: https://raytracing.github.io/books/RayTracingInOneWeekend.html, with these caveats:

1. Haven't optimized the performance yet (especially in the Pluto.jl version!)
2. The refraction of negatively-scaled spheres doesn't look right, yet
3. I didn't render the final scene... the camera seems to point in the wrong area... so probably some bug left there.