DOC: Add algorithm references to function docstrings

[nawtrey]

When the pseudocode algorithms are finished for the partial, directional, and flux diagram generation functions it would be good to add references to these in the corresponding docstrings.

[nawtrey]

This is probably best handled once the KDA paper is published so I can add the actual citation to the documentation.

[nawtrey]

With 61a1fcb merged I think this issue is on the path to being closed. I've already spent some time working on changes for the partial diagrams algorithm, and the flux diagrams algo is likely to change soon as well, so I don't think adding these labels to the documentation will be of any real use.