Round to square connector

This provides a connector between a square-ended tube and a round-ended tube. It is an application of the superellipse http://en.wikipedia.org/wiki/Superellipse. The script makes use of the fact that the superellipse family of curves encompassed both a square and a circle, so smooth morphing between the two can be achieved parametrically. The derivation of the script is discussed in my blog http://kitwallace.posterous.com/piet-hein-and-the-superegg