Source Code Documentation

[NBajanca]

I've come across this problem when trying to use intersphinx.
The module index doesn't exist and there is no link from the documentation to the source code.

While the use cases in the documentation are useful to get the user going I think it lacks a connection to the code.

At least for me (I think this is the third issue I open in two weeks and the other two were posted mainly for lack of knowledge on this library) a documentation connected to the code would be interesting. Even for you (@omab), because a better understanding of the library leads to better and more contributions.