6 functions for generating artificial datasets

* twospirals.m generates two classes representing two spirals
* clusterincluster.m generates two circular classes
* corners.m generates four classes, each corresponding to a corner shape pointing towards the center
* halfkernel.m generates two half ellipses, one inside the other
* crescentfullmoon.m generates one circular class and one larger crescent folded around it.
* outlier.m produces 2 large circular classes, and 2 smaller classes of outliers.

Inspired by the following StackOverflow question:
http://stackoverflow.com/questions/16146599/create-artificial-data-in-matlab