Added Ring Shape

Ring shape—circle with hollow center.

![screen shot 2013-12-13 at 2 01 33 am](https://f.cloud.github.com/assets/3374510/1740383/8a57704a-63c5-11e3-8804-adecd20f919f.png)

![image](https://f.cloud.github.com/assets/3374510/1740387/9a562c3e-63c5-11e3-9e3c-4451b4e242ad.png)