add demo

src/experimental/demo/nz_voronoi3_demo.scad

@@ -0,0 +1,21 @@
+use <experimental/nz_voronoi3.scad>;
+
+size = [20, 20, 20];
+dim = 2; 
+seed = 1;
+
+points = [
+    for(z = [0:size[2] - 1]) 
+        for(y = [0:size[1] - 1]) 
+            for(x = [0:size[0] - 1]) 
+                [x, y, z, nz_voronoi3(size, x, y, z, seed, dim)]
+];
+
+max_dist = max([for(p = points) p[3]]);
+
+for(p = points) {
+    c = p[3] / max_dist * 2;
+    color([c > 1 ? 1 : c , 0, 0])
+    translate([p[0], p[1], p[2]])
+        cube(1);
+}