Major re-write of triangulation in matplotlib

Ian Thomas has been working on including some of the functionality from Qhull into the matplotlib triangulation pipeline (

After a thorough development and testing cycle this PR has now been merged onto master, but I just wanted to give a shout-out to anybody who uses triangulation in earnest so that you can give this new functionality a go before we cut a release candidate for v1.4 on the 8th of January 2014.

If you encounter any problems, please feel free to open a github issue which mentions @ianthomas23.