updated docs

docs/lib-cross_sections.md

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+# cross_sections
+
+Given a starting cross-section, points and angles along the path, this function will return all cross-sections. Combined with the `polysections` module, you can create a specific path extrusion.
+
+It depends on the `rotate_p` function. Remember to include "rotate_p.scad".
+
+## Parameters
+
+- `shape_pts`: A list of points represent a shape. See the example below.
+- `path_pts` : A list of points represent the path.
+- `angles` : A list of angles. Each point should have a corresponding angle used to rotate the 2D shape.
+- `twist`: The number of degrees of through which the shape is extruded.
+- `scale` : Scales the 2D shape by this value over the length of the extrusion. Scale can be a scalar or a vector.
+
+## Examples
+
+	include <rotate_p.scad>;
+	include <polysections.scad>;
+	include <cross_sections.scad>;
+	include <archimedean_spiral.scad>;
+
+	shape_pts = [
+		[-2, -10],
+		[-2, 10],
+		[2, 10],
+		[2, -10]
+	];
+
+	pts_angles = archimedean_spiral(
+		arm_distance = 20,
+		init_angle = 180,
+		point_distance = 5,
+		num_of_points = 100 
+	); 
+
+	pts = [for(pt_angle = pts_angles) pt_angle[0]];
+	angles = [
+		for(i = [0:len(pts_angles) - 1]) [90, 0, pts_angles[i][1]]
+	];
+
+	polysections(
+		cross_sections(shape_pts, pts, angles, twist = 180, scale = 0.1)
+	);
+
+![cross_sections](images/lib-cross_sections-1.JPG)