Cellular automaton snowflake generator in OpenSCAD

By default this cellular automaton uses [Stephen Wolfram's rule](http://www.wolframscience.com/nks/p371--the-growth-of-crystals/) that a filled cell stays filled and an unfilled one becomes filled if it has exactly one filled neighbor.

You can vary the rules and even include indeterministic rules. For instance, one can set chance the probability of generation when there is one neighbor to 0.5, so the generation parameters are 0,0.5,0,0,0,0,0. These more snowflake-like to me than the defaults