add differential_line_growth

examples/differential_line_growth.scad

@@ -0,0 +1,18 @@
+use <shape_circle.scad>;
+use <experimental/differential_line_growth.scad>;
+    
+$fn = 24;
+r = 20;
+times = 50;
+thickness = 2;
+node_option = [
+    0.5,    // maxForce 
+    0.7,    // maxSpeed
+    12,     // separationDistance
+    1.5,    // separationCohesionRatio 
+    10      // maxEdgeLength
+];
+
+init_shape = shape_circle(r);
+linear_extrude(thickness)
+    polygon(differential_line_growth(init_shape, node_option, times));