analogs of graph-theoretic / network-analytic measures

[corybrunson]

There's some mileage to be got from adapting concepts from graph theory and network analysis to the analysis of simplicial complexes, whether simulated or constructed from data. This paper provides a good survey, including

• degree, distance, and other tools to measure centrality
• clustering coefficients and other measures of neighborhood closure
• community detection and evaluation

These are not priorities for me, but they seem worth adding in the medium term, and they might make good student projects or first issues since (i expect) many could be done in R using the (amazing) traversals provided in simplextree.

[peekxc]

I think this would be a welcome addition to the package. I originally meant to make functions like degree accept the same inputs as the other functions (list of simplices, column matrix of d-simplices, etc.) but after realizing that there might be multiple interpretations of the 'degree' of a non-0 simplex I choose to just stick with vertices for time sake