Implement 2048 in Python!

Possible TODO:
* The code in apply_move() could probably be cleaned up.
* Colorized terminal output.
* Command-line options for board size, target tile.
* Implement game logic as a module, so different UI can be wrapped
  around it, e.g. wxPython, text-mode, ...
* Unit tests.
* Sound.
* 3-D or n-D boards.
* Non-rectilinear board (e.g. hexagonal).
* getch() on Windows?

Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>