Code for co-author network from ESA program.

The code I added mines the ESA website data to generate an edgelist of co-authors.  I've included the code to generate this, and the generated data, and a file doing some initial explorations.  I have more to say about this that I'll include in an issue in the main repo.

Given the small number of co-authors, I suggest that you give us contributor access rather than managing the project with pull requests.