Register VennEuler

This is a very-much-work-in-progress library for computing and rendering area-proportional Euler diagrams, based on a rather brute-force algorithm by Wilkinson. Here's an example of what it generates, using 3-DoF rectangles:

![Polyglot Programming DC overlap](http://photos4.meetupstatic.com/photos/event/3/b/9/4/highres_396195252.jpeg)