added rounded_extrude

docs/lib-rounded_extrude.md

@@ -0,0 +1,28 @@
+# rounded_extrude
+
+Extrudes a 2D object roundly from 0 to 180 degrees. 
+
+## Parameters
+
+- `size` : The size of A retangle which can cover the 2D object. Accepts single value, square with both sides this length. It also accepts 2 value array `[x, y]`, rectangle with dimensions `x` and `y`.
+- `round_r` : The radius when extruding roundly.
+- `angle` : 0 to 180 degrees. The default value is 90 degrees. 
+- `convexity`, `twist`: The same as respective parameters of `linear_extrude`.
+- `$fa`, `$fs`, `$fn` : Used to control the round fragments. Check [the circle module](https://en.wikibooks.org/wiki/OpenSCAD_User_Manual/Using_the_2D_Subsystem#circle) for more details.
+
+## Examples
+
+	include <rounded_extrude.scad>;
+
+	$fn = 48;
+
+	circle_r = 10;
+	round_r = 5;
+
+	rounded_extrude(circle_r * 2, round_r) 
+		circle(circle_r);
+		
+	translate([0, 0, round_r]) 
+		cylinder(h = 20, r1 = circle_r + round_r, r2 = 0);
+
+![rounded_extrude](images/lib-rounded_extrude-1.JPG)