Added Shape AnnularSection

AnnularSection is a section of an annulus (ring)
http://en.wikipedia.org/wiki/Annulus_%28mathematics%29

![screen shot 2013-12-12 at 10 48 02 pm](https://f.cloud.github.com/assets/3374510/1739743/8de44b8c-63a9-11e3-942e-901a6f66c819.png)