add doc

README.md

@@ -147,7 +147,7 @@ See [examples](examples).
 - Point Transformation (2.3 Preview)
     - [ptf/ptf_rotate](https://openhome.cc/eGossip/OpenSCAD/lib2x-ptf_rotate.html)
     - [ptf/ptf_x_twist](https://openhome.cc/eGossip/OpenSCAD/lib2x-ptf_x_twist.html)
-	- ptf/ptf_y_twist
+	- [ptf/ptf_y_twist](https://openhome.cc/eGossip/OpenSCAD/lib2x-ptf_y_twist.html)
 	- ptf/ptf_circle
 	- ptf/ptf_bend
 	- ptf/ptf_ring

docs/lib2x-ptf_y_twist.md

@@ -0,0 +1,42 @@
+# ptf_y_twist
+
+Twist a point along the y-axis. You can use it to create something such as a [twisted maze](https://github.com/JustinSDK/dotSCAD/blob/master/examples/maze/twisted_maze.scad).
+
+![ptf_y_twist](images/lib2x-ptf_y_twist-2.JPG)
+
+**Since:** 2.3.
+
+## Parameters
+
+- `size` : 2 value array `[x, y]`, rectangle with dimensions `x` and `y`.
+- `point` : The point to be twisted.
+- `angle` : The number of degrees.
+
+## Examples
+
+    use <hull_polyline3d.scad>;
+    use <ptf/ptf_y_twist.scad>;
+
+    size = [10, 20];
+
+    rows = [
+        for(y = [0:size[1]])
+            [for(x = [0:size[0]]) [x, y]]
+    ];
+
+    columns = [
+        for(x = [0:size[0]])
+            [for(y = [0:size[1]]) [x, y]]
+    ];
+
+    for(line = rows) {
+        twisted = [for(p = line) ptf_y_twist(size, p, 90)];
+        hull_polyline3d(twisted, thickness = .1);
+    }
+
+    for(line = columns) {
+        twisted = [for(p = line) ptf_y_twist(size, p, 90)];
+        hull_polyline3d(twisted, thickness = .1);
+    }
+
+![ptf_y_twist](images/lib2x-ptf_y_twist-1.JPG)

src/ptf/ptf_y_twist.scad

@@ -1,10 +1,15 @@
+/**
+* ptf_y_twist.scad
+*
+* @copyright Justin Lin, 2020
+* @license https://opensource.org/licenses/lgpl-3.0.html
+*
+* @see https://openhome.cc/eGossip/OpenSCAD/lib2x-ptf_y_twist.html
+*
+**/ 
+
 use <ptf/ptf_rotate.scad>;
 
-/*
-    size: The size of a rectangle.
-    point: A point in the rectangle.
-    angle: twisted angle.
-*/
 function ptf_y_twist(size, point, angle) =
     let(
         xlen = size[0],