Last version without database

v0.2.7

update docs to 0.2.7

First version as mgrid

• planar graph
• supra graph

Final version for "vsec"

• Basic cut-related features
• Remove unnecessary methods.

Full-fledged version for vertex-splitting

• Only one class.
• Store using networkx directed graph.
• Two methods to update associated dataframes.
• Ignore edge contraction for now.
• Basic features for components, when new edges serve as cuts.

First workable version

• Features for edge contraction are not complete.
• Data for fixture case_grid has not been uploaded.