added polyline3d

docs/lib-polyline3d.md

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+# polyline3d
+
+Creates a polyline from a list of `[x, y, z]` coordinates. It depends on the `line3d` module so you have to `include` line3d.scad.
+
+## 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.
+- `startingStyle` : The end-cap style of the starting point. The value must be `CAP_BUTT`, `CAP_CIRCLE` or `CAP_SPHERE` (defined in line3d.scad). The default value is `CAP_CIRCLE`. 
+- endingStyle : The end-cap style of the ending point. The value must be `CAP_BUTT`, `CAP_CIRCLE` or `CAP_SPHERE` (defined in line3d.scad). The default value is `CAP_CIRCLE`.
+- `fn` : It controlls the `$fn` value used by the `circle` and `sphere` module. The default value is `24`.
+
+## Examples
+
+	polyline3d(
+	    points = [
+	        [1, 2, 1], 
+	        [-5, -4, 2], 
+	        [-5, 3, 3], 
+	        [5, 5, 4]
+	    ], 
+	    thickness = 1
+	);
+
+![polyline3d](images/lib-polyline3d-1.JPG)
+
+	polyline3d(
+	    points = [
+	        [1, 2, 1], 
+	        [-5, -4, 2], 
+	        [-5, 3, 3], 
+	        [5, 5, 4]
+	    ], 
+	    thickness = 1,
+	    endingStyle = CAP_SPHERE
+	);
+
+![polyline3d](images/lib-polyline3d-2.JPG)
+
+	polyline3d(
+	    points = [
+	        [1, 2, 1], 
+	        [-5, -4, 2], 
+	        [-5, 3, 3], 
+	        [5, 5, 4]
+	    ], 
+	    thickness = 1,
+	    startingStyle = CAP_SPHERE,
+	    endingStyle = CAP_SPHERE
+	);
+
+![polyline3d](images/lib-polyline3d-3.JPG)
+
+	r = 20;
+	h = 5;
+	fa = 15;
+	circles = 10;
+	
+	points = [
+	    for(a = [0:fa:360 * circles]) 
+	        [r * cos(a), r * sin(a), h / (360 / fa) * (a / fa)]
+	];
+	polyline3d(points, thickness = 1);
+
+![polyline3d](images/lib-polyline3d-4.JPG)