Javascript Ray Marcher v0.6

Coloured lights! Now it looks like a real ray-tracer. Ray marcher. Whatever.

Coloured lights are the start of the colour system, and a great way to test that everything else is working just fine. In this case, everything is not fine due to the colour banding, but I'll hammer that out when I deal with things like the maximum brightness and materials.

(Edit) The banding was not caused by maximum brightness or materials, but was a bug in the fundamental ray cast routine. I fix it in a later version, but I'm preserving it here for the educational value.