Figure out what to do with GraphMaze

[sraaphorst]

As it stands, GraphMaze is hardly a proof of concept, but since Maze has a monomorphism to ThickMaze, and ThickMaze has a monomorphism to GraphMaze, clearly GraphMaze is the most powerful and flexible formulation of the three.

It would be nice if we can somehow use this to work on mazes that are not a rectangular area of the plane.

Regardless, a GenerateGraphMaze is needed, as are test cases.

[sraaphorst]

This is essentially the same issue as #125.