WIP:  Documentation Improvements

Preview:
http://www.stsci.edu/~lbradley/photutils/
I don't know if this is the reason, but there's something wrong with the navigation (see http://www.stsci.edu/~lbradley/photutils/photutils/psf.html and the screenshot)
![screen shot 2014-12-02 at 17 03 03](https://cloud.githubusercontent.com/assets/852409/5265784/53ba7e82-7a45-11e4-823c-1d32a6f6cbc8.png)