Javascript Ray Marcher v0.8

The big improvement for this version is a preview render! The renderer does a fast, low-resolution scan before doing the full render. It's a good way for me to see that the the scene is working correctly before I wait for an hour to get the final version.

And it is also cleanup time. I've added Javascript objects to hold the raytracer objects. Now all the properties for the objects are in the same place, and adding new objects is much easier.

I added rotation to vectors, and the code to rotate the camera.

Actually, wait, the big improvement is adding mirrored surfaces. That's important. It's also easy, because it is basically the same code for shadows, but instead of firing a second ray at a light, I fire a second ray at the correct bounce angle.

Now I can do scenes of placid lakes in the mountains, reflecting the starry sky above. I really need to get to work on that one, instead of the "green ball on a mirror"