Move away initial reg alloc "code notes".
Add empty() method for IGraph hierarchy.
Start DigraphAdjList implementation, and otherwise extend API.
neighs()/degree() methods for new class hierarchy.
Elaborate DigraphAdjList impl, add UngraphAdjList.
Further elaborate new hier API, add node attr support.
Add from_neigh_list() and __eq__().
Use set instead of list for neighbor nodes.
Typo fix (raise instead of return).
Use new graph API for graph coloring.
Update for new graph API.
Remove old graph implementation.