Code for display and traversal of networkx graphs.

- Implemented basic BFS using the networkx.Graph object.
- Used above implementation to search for (weightless) shortest
  paths along a graph representation of the USA.
- Displayed the above graph and the paths in an intuitive graphical
  form, using matplotlib and the nx.draw() function.
Add basic python implementation of Bellman-Ford.

- Implemented the Bellman-Ford algorithm using the
  networkx.DiGraph object. support for nondirected graphs is pending.