custom_extrude for openscad

module polygon_custom_extrude(points, height, layer=0.1)
for non-linear extrude for polygon.

example functions for scaling and rotating in polygon_custom_extrude:

function fscale(z) = 1+0.5*sin(180*1.82*z); // sinus
//function fscale(z) = 2*(1-pow(z,2)); // parabola

function ftwist(z) = sin(180*3*z)*30*z; // sinus
//function ftwist(z) = 60*z; // linear
//function ftwist(z) = 0; // no twist