make advanced topics a flat list

this restructures the advanced topics into a flat list vs trying to group them, i.e. one page per topic.

I think the content is more exposed and readable this way.

Also, I removed a few of the empty stub sections that I didn't think were going to be filled in any time soon.  I think they were giving a negative impression to the guide as a whole.  Notable exceptions are the "Application Deployment" and "Patching and Forking" topics which I plan to work on soon.

you can see the built version here:  http://python-packaging-user-guide.readthedocs.org/en/advanced/additional.html