add doc

docs/lib2-px_circle.md

@@ -6,7 +6,7 @@ Returns points that can be used to draw a pixel-style circle.
 
 ## Parameters
 
-- `radius` : The circle radius.
+- `radius` : The circle radius. The value must be an integer.
 - `filled` : Default to `false`. Set it `true` if you want a filled circle.
 
 ## Examples

docs/lib2-px_cylinder.md

@@ -6,10 +6,10 @@ Returns points that can be used to draw a pixel-style cylinder.
 
 ## Parameters
 
-- `radius` : The radius of the cylinder. It also accepts a vector `[r1, r2]`. `r1` is the bottom radius and `r2` is the top radius of a cone.
+- `radius` : The radius of the cylinder. It also accepts a vector `[r1, r2]`. `r1` is the bottom radius and `r2` is the top radius of a cone. Values must be an integer.
 - `h` : The height of the cylinder or cone. 
 - `filled` : Default to `false`. Set it `true` if you want a filled cylinder.
-- `thickness`: Default to 1. The thickness when `filled` is `false`.
+- `thickness`: Default to 1. The thickness when `filled` is `false`. The value must be an integer.
 
 ## Examples
 

docs/lib2-px_sphere.md

@@ -0,0 +1,22 @@
+# px_sphere
+
+Returns points that can be used to draw a pixel-style sphere.
+
+**Since:** 2.0
+
+## Parameters
+
+- `radius` : The radius of the sphere. The value must be an integer.
+- `filled` : Default to `false`. Set it `true` if you want a filled sphere.
+- `thickness`: Default to 1. The thickness when `filled` is `false`. The value must be an integer.
+
+## Examples
+
+	include <pixel/px_sphere.scad>;
+
+	for(pt = px_sphere(10)) {
+		translate(pt)
+			cube(1, center = true);
+	}
+
+![px_sphere](images/lib2-px_sphere-1.JPG)