Implemented a couple of simple DFS and BFS graph exploration algorithms.
These basically traverse the graph. Will need to add visitors which can
help us do something useful based upon a traversal to each vertex in the
graph. For now this doesn't do much more than tell us whether a target
vertex can be reached from a source given an undirected graph.
Merge branch 'master' of https://github.com/arvindpereira/data-structs-algorithms.git