3D function plotter for Customizer / OpenSCAD

This is an easy to use 3D surface plotter. Use the Customizer to change the function plotted and the range.

To use in your own code, call `graphFunction3D(function,minX,minY,maxX,maxY)` where the function is a string such as "exp(-x^2-y^2)" (for more details, see [here](http://www.thingiverse.com/thing:2295309)). By default a surface of smallish thickness is drawn. Here are some options:

* `surfaceThickness=dz`: change the thickness of the surface
* `flatMinimumThickness=dz`: does a flat-bottomed graph; dz specifies the minimum thickness (set to 0 for an automatic smallish thickness)
* `bottomFunction=f`: specifies a function for the bottom of the graph

There are also `makePointList()` and `makeFaceList()` functions that generate the arguments for a `polyhedron()`.

This demonstrates and uses my [function parser](http://www.thingiverse.com/thing:2295309). The standalone version bundles the parser.

**Update:** May 17, 2017: Rewrote to generate whole polyhedron at once an