surf2solid

Conversion routines to take a surface (a function z of (x,y) or (theta,r)) and convert this into a solid; much as meshz does, but a little more useful for outputting as an STL for frabrication in a 3D printer. There are two cases, one in Cartesian co-ordinates, and the other in polar co-ordinates. Plus two sets of examples to show how they are used.