add doc

README.md

@@ -210,6 +210,9 @@ See [examples](examples).
 - [util/sum](https://openhome.cc/eGossip/OpenSCAD/lib2x-sum.html)
 - [util/zip](https://openhome.cc/eGossip/OpenSCAD/lib2x-zip.html)
 
+### Turtle
+- [turtle/footprints2](https://openhome.cc/eGossip/OpenSCAD/lib2x-footprints2.html)
+
 ----
 
 ## Bugs and Feedback

docs/lib2x-footprints2.md

@@ -0,0 +1,54 @@
+# footprints2
+
+Drive a turtle with `["forward", length]` or `["turn", angle]`. This function is intended to use a turtle to imitate freehand drawing. 
+
+**Since:** 2.4
+
+## Parameters
+
+- `cmds` : A list of `["forward", length]`s and `["turn", angle]`s.
+- `start` : Set the start point of the turtle.
+
+## Examples
+	    
+	use <polyline2d.scad>;
+	use <turtle/footprints2.scad>;
+	
+	function arc_cmds(radius, angle, steps) = 
+		let(
+			fa = angle / steps,
+			ta = fa / 2,
+			leng = sin(ta) * radius * 2
+		)
+		concat(
+			[["turn", ta]],
+			[
+				for(i = [0:steps - 2])
+				each [["forward", leng], ["turn", fa]]
+			],
+			[["forward", leng], ["turn", ta]]
+		);
+		
+	poly = footprints2(
+		concat(
+			[
+				["forward", 10],
+				["turn", 90],
+				["forward", 10] 
+			], 
+			arc_cmds(5, 180, 12),
+			[
+				["turn", -90],
+				["forward", 10],
+				["turn", 90],
+				["forward", 10],
+				["turn", 90],
+				["forward", 10]
+			]
+		)
+	);
+
+	polyline2d(poly, width = 1);
+
+![t3d](images/lib2x-footprints2-1.JPG)
+

src/turtle/footprints2.scad

@@ -1,51 +1,16 @@
-use <turtle2d.scad>;
+/**
+* footprints2.scad
+*
+* @copyright Justin Lin, 2020
+* @license https://opensource.org/licenses/lgpl-3.0.html
+*
+* @see https://openhome.cc/eGossip/OpenSCAD/lib2x-footprints2.html
+*
+**/ 
+
 use <_impl/_footprints2.scad>;
+use <turtle2d.scad>;
 
-/*
-    cmds: "turn", "forward"
-
-demo code
-```
-use <turtle/footprints2.scad>;
-use <hull_polyline2d.scad>;
- 
-function arc_cmds(radius, angle, steps) = 
-    let(
-        fa = angle / steps,
-        ta = fa / 2,
-        leng = sin(ta) * radius * 2
-    )
-    concat(
-        [["turn", ta]],
-        [
-            for(i = [0:steps - 2])
-            each [["forward", leng], ["turn", fa]]
-        ],
-        [["forward", leng], ["turn", ta]]
-    );
-    
-poly = footprints2(
-    concat(
-        [
-            ["forward", 10],
-            ["turn", 90],
-            ["forward", 10] 
-        ], 
-        arc_cmds(5, 180, 12),
-        [
-            ["turn", -90],
-            ["forward", 10],
-            ["turn", 90],
-            ["forward", 10],
-            ["turn", 90],
-            ["forward", 10]
-        ]
-    )
-);
-
-hull_polyline2d(poly, width = 1);
-```
-*/
 function footprints2(cmds, start = [0, 0]) = 
     let(
         t = turtle2d("create", start[0], start[1], 0),