Added graphhopper, graphhopper-sna, trove dependencies.
Calculate closeness using graphhopper(-sna).
Add methods for loading GH graphs from data sets.
Update pom.
Make ST_ClosenessCent... parse optional arguments.
Fix pom.
Fix minor errors.
Update unit tests.
Rename Undirected... to Unweighted...
Fix method name.
Remove jgrapht-sna centrality computations.
Update dependencies in pom.
Update gitignore.
Fix some dependencies.
Compute closeness on weighted graphs.
Add tests for Nantes in comments.
Add classes for parsing SQL function arguments.
Revise how SQL function parameters are parsed.
Add default values and update function signatures.
Clean up code.