Added option to output directed graphs of the group heirarchy before and after compression

[Azrenbeth]

BUILDS ON azren/wrapped_in_pyo3 (PR #42)

Added a -g option which creates a set of 4 files:

• before_edges.csv
• before_nodes.csv
• after_edges.csv
• after_nodes.csv

These files are a representation of the state groups and their predecessor links. They can be viewed in something like Gephi.

[rubo77]

Could you add an example screenshot?