Inflate triangular mesh library for OpenSCAD

This library lets you inflate 2D polygons into the third dimension, e.g., making them be thin around the edges and fat in the middle (as well as more complex effects). For instance, you can take a square and inflate it to look like a pillow.

You need my [eval library](https://www.thingiverse.com/thing:2295309) as well.

Usage is a bit complicated.

* Your initial polygon needs to be triangulated: you can use my [triangulation library](https://www.thingiverse.com/thing:4413843) to triangulate it and then refine the triangulated mesh for the resolution you require.

* Then you specify a function for the bottom of the inflated polygon and another for the top. These functions can depend on three variables: x, y and d, where [x,y] are the coordinates in the mesh and d is the distance from the mesh edge. The functions are passed as strings to the inflation, e.g., ("3*pow(d,0.5)"), using the variant subset of the OpenSCAD formula language supported by my eval library.

The main