Gut the project and start over with rspec --init and a Rakefile.

My goal on this branch is to re-build the breadth-first search spike from scratch using TDD/BDD.
Add the original problem's tests as an acceptance spec.

* Skeleton maze class
* All acceptance specs marked pending until they can pass
Add very basic maze parsing and cell access.
Require spec_helper in specs.
Maze collaborates with a solver to solve itself.

* Solver isn't fleshed out yet, but its API is fleshed out using mocks
* Solutions are simple arrays for now
* Not happy with the duplication in maze_spec
Simplify mazes in maze_spec.
Solve mazes that only require one step.
Solve general mazes with recursion.

* Passes all acceptance tests.
* Not a great solution yet.
Don't yield off-grid neighbors.
Use breadth-first search instead of depth-first search.

This guarantees that the shortest solution will be the first solution found.
Introduce a Cell object to encapsulate the ASCII symbols.
Rename block params that shadow method params.
Cells know their position in the maze.
Delegate neighbor_positions to Cell.
Cell knows its maze and can find its own neighbors.
Extract traversable_neighbors to Cell.
Extract a Path to wrap the solution arrays.
Extract a queue-like private API in solver.
Paths know their own successors.
Minor cleanups.