added hull_polyline3d

docs/lib-hull_polyline3d.md

@@ -0,0 +1,41 @@
+# hull_polyline3d
+
+Creates a 3D polyline from a list of `[x, y, z]` coordinates. As the name says, it uses the built-in hull operation for each pair of points. It's slow. However, it can be used to create metallic effects when the `fn` parameter is small.
+
+## Parameters
+
+- `points` : The list of `[x, y, z]` points of the polyline. : A vector of 3 element vectors. The points are indexed from 0 to n-1.
+- `thickness` : The line thickness.
+- `fn` : It controlls the `$fn` value used by the `sphere` module. The default value is `3`.
+
+## Examples
+
+	hull_polyline3d(
+	    points = [
+	        [1, 2, 3], 
+	        [4, -5, -6], 
+	        [-1, -3, -5], 
+	        [0, 0, 0]
+	    ], 
+	    thickness = 1, 
+	    fn = 3
+	);
+
+![polyline3d](images/lib-hull_polyline3d-1.JPG)
+
+	r = 50;
+	points = [
+	    for(a = [0:180]) 
+	        [
+	           r * cos(-90 + a) * cos(a), 
+	           r * cos(-90 + a) * sin(a), 
+	           r * sin(-90 + a)
+	        ]
+	];
+	
+	for(i = [0:7]) {
+	    rotate(45 * i) 
+	        hull_polyline3d(points, 2, 3);
+	}
+
+![polyline3d](images/lib-hull_polyline3d-2.JPG)