Add modules page that documents the module interaction.

Includes a graph made by graphviz with fancy URL's to the rest of the documentation.

To test:

1. check out this branch
2. Make sure you have graphviz installed
3. cd docs
4. make html
5. In a browser, go to file:///docs/build/html/modules.html

Also fix OCSPAdder docstrings and add that to the index.

Closes #6 (closed)