Added RadialRug

I saw that geometric rugs were in the feature requests, so I implemented a decent version of them.  A radial rug is more interesting that a checkered rug because it's radially-symmetric.  Each quadrant of the rug is symmetrical with the other quadrants.  I attached some screenshots to this, too.
![rug3](https://f.cloud.github.com/assets/2229288/1433297/3c532c9c-40f0-11e3-998e-1c0090768915.png)
![rug1](https://f.cloud.github.com/assets/2229288/1433298/3e38e146-40f0-11e3-8103-d6b8c5c6b1b0.png)
![rug2](https://f.cloud.github.com/assets/2229288/1433299/4047e658-40f0-11e3-8832-3a3d7b3e04de.png)