Roxygen demo for one function

I suggest we work in roxygen for documentation. It makes it a lot easier/faster to build and document new functions. If you guys want to, we can start working through the functions, or just do this for the new ones. It won't re-write existing unless there is roxygen syntax in the file. 
![image](https://cloud.githubusercontent.com/assets/2349007/3271114/2093e6de-f308-11e3-887a-197d9da2dc0c.png)