add retro random walker example

examples/retro-random-walker/turtle.js

@@ -0,0 +1,30 @@
+function turtle(){
+ retro()
+
+  for (let j = 0; j < 10; j++){
+
+  penup()
+  setpos(0,0)
+  pendown()
+
+      for (let i = 0; i < 2000; i++){
+	
+	penSize(randint(30))
+	
+	if (randint()<50)
+	{
+	  penup()
+	} else 
+	{
+	  pendown()
+	}
+
+	  forward(randint())
+	  right(randint())
+
+
+    }
+
+  }
+}
+