OpenScad Surface Solids 1.2

I was sitting around the kitchen table wondering how I could model a playground slide, or those water slide tubes.

This thing adds hermite curve/surface support to the OpenScad Surface Solids library.

The basic Hermite interpolation calculation has actually been lurking for a while, but now it's put to good usage. With this, there is now a lerp (linear interpolation), berp (bezier interpolation), and herp (hermite interpolation) in the library.

A Hermite curve is defined by two endpoints, and the tangent vectors to those points. It is somewhat related to a Bezier curve. In fact, I use the same Bernstein basis functions to express it. Some people may find it easier to deal with, some harder, but it's just another tool in the box to help you create surfaces.

In this particular case, I've added a 'sweep_hermite()' module to the renderer. This is really easy to work with. You define one curve to be your 'profile', and you define another curve to be the path along which yo