Create a set of equally spaced mesh contours.

Input parameters:

1. Ms → Mesh to contour.
2. Pt → Contour base point.
3. Nr → Contour slice normal direction.
4. Sp → Spacing between contour layers.

Output parameters:

1. Ct → Contour polylines, sorted by layer.
2. Ly → Layer, i.e. contour section offset, given as an integer. Layer zero is the section through the base point.