ray tracing in another weekend

I'm still playing around with Ray Tracing In One Weekend, this time by re-writing it in C. I wanted to implement this on CPU and play around with a little more than what my WebGL implementation had to offer. This way, I can do stuff like render a bunch of frames in a for loop and use ffmpeg to glue them together into a video (with a cool boomerang effect too)!

I've got some code cleanup and performance improvements to take care of, and then I'll move on to The Next Week.