Set up initial maze builder/solver

Running `ruby maze.rb` in the terminal, creates a new maze, showing each
step in generating the maze, then shows a solution to the maze step by
step. Currently, walls are represented by 'W's, regular nodes by an
empty space, and a node which was visited while solving the maze by an
'o'. Each step is elegantly displayed by "putsing" the maze, sleeping
for a short time, then clearing the terminal window.