OpenScad Surface Solids

The 1.0 version of the Bezier library included a simple linear extrusion of the bezier surface. The things this derives from added a quick and easy 'shell extrusion', which took into account the normals on the quads to create true 'inner' and 'outer' quads.

This thing makes a few improvements to both the normal calculations, and rearranges the libraries slightly to accomodate for future curved surface/solid things.

As a bonus, the hermite.scad file is thrown in. At the moment, it only has basic Hermite calculations. It even has a surface thing. So, if you want to play with that, here it is.

Also, in terms of library function naming, I've switched to being more explicit and rational.

linear_extrude_bezier - extrusion in the z-axis
shell_extrude_bezier - extrusion along the normals

So, for Hermite, it would be linear_extrude_hermite, shell_extrude_hermite

One of the cool features is the ability to show the normals, per vertex. This is extremely handy for debugging