Scalable Painter's Tetrahedron/Triangle/Pyramid/Cone

This is a painter's tetrahedron in openscad.  It is scalable using the parameter "scale_factor".  You can also set the thickness of the sides and the length of the side.  Really, "scale_factor" and "thick" are the only two you'll ever need to adjust.  As you scale up a pyramid, sometimes the side of the pyramid gets thicker than you probably want. Just resize "thick" to make it thinner.