Normal Bezier surface experiment

Not that http://www.thingiverse.com/thing:8786 isn't normal, just that it does not extrude along the surface normal.

Both ways of extrusion can be useful, this one handles zig-zags correctly. Also, joining surfaces is seamless when the edge and inner control points are collinear.

Only made possible by the brilliant work of WilliamAAdams.