Fit text to arbitrary surface in OpenSCAD

This uses my [Hershey fonts](https://www.thingiverse.com/thing:2404566) and [function evaluation](https://www.thingiverse.com/thing:2295309) libraries to provide a module that fits text to an arbitrary surface with arbitrary distortion (i.e., uv mapping). See the demo code in maphershey.scad.

If you want to use this in production, download the latest Hershey and eval libraries from their own pages, rather than relying on the ones bundled in the mapshershey-standalone.scad file.

Usage: