Fan geometry

This is not ready to be merged yet, but I'm opening this up for some early feedback.  This introduces a FanGeometry and FanOutlineGeoemtry (and all of the CZML trimmings).  A Fan is defined by an origin, radius, and list of directions.  The outline also has an optional number of rings to draw.  This is useful for drawing any kind of static, projected shape; such as an azimuth and elevation mask or body masks.

![image](https://cloud.githubusercontent.com/assets/1495196/2611455/a9baf84e-bba4-11e3-8f7d-b6f7ca0b8808.png)

![image](https://cloud.githubusercontent.com/assets/1495196/2611454/9fadb7b0-bba4-11e3-894d-4c90519d6c17.png)

@pjcozzi or @bagnell it would be great if one of you could check out FanGeometry.js and FanOutlineGeometry.js and let me know what, if anything I'm doing wrong.  I originally implemented the geometry as a TRIANGLE_FAN, but changed it to TRIANGLES because it let me use the GeometryPipeline helper functions.

I'm almost 100% certain my st generation is wrong, but I'm completely at a loss there since I've never done it before and I also am not sure how the texturing should behave, I imagine it should be like a crumpled up piece of paper.

@emackey You'll probably be interested in this as well.

Here's my to-do list.
- [x] Clean up documentation
- [x] Sandcastle example
- [x] Write specs
- [x] Fix FanGeometry st generation.