Add Hero.Game and Hero.UI modules.

The Hero.UI module is responsible for interacting with the external
state (i.e., NCurses) from the game loop.

The Hero.Game module is repsonsible for setting up the game and running
it. The gameLoop function is the core logic loop of the game.
Add a win condition (reach the down stairs).

Add the Direction type which corresponds to a cardinal direction.

Add the move function which determines where moving in a direction from
a point will result.