add second ring of prisms to the scene
add SoapBubbleMaterial
add soap bubbles to scene
add walls to scene

The scene has now been completely ported from Luculentus. Aside from
a few minor things, the port is complete.
take lodepng from its original repository

I forked lodepng-rust to Cargoify it. The author has merged my pull
request, so now the original repository can be used with Cargo.
add simple performance counter