OpenScad Revoloids version 0.6

Well, revoloids (slight change in name) are really nifty cool, easy to generate surfaces in a mathematical sense, but for them to be relevant to 3D printing, they need some volume.

This thing adds the ability to specify a thickness on your revoloid so that you can actually export as a .stl and print it.

I whimped out (and thus still not 1.0) and just used the normal of the circle to calculate the second quad. The actual normal is a cross between the tangent of the circle, and the tangent of the curve at that point. Next version.

I also want to come up with a nice scheme for printing flats for 'bottoms' and 'tops'.