This simplifies the code in many places, and allows inheritance of the
game mode classes (Training, Duplicate and FreeGame).
- A Tile is no more an unsigned char, but a class: it should help supporting
i18n of the game. The Dic library still uses unsigned chars though.
- Improved the configure script, to enable/disable the compilation of some
interfaces.
- Added a ncurses interface, much nicer than the text one. The game mode and
the number of players are currently hardcoded, it is not possible to change
them interactively (yet).
- Repaired the save/load functions.
NOTE: The wxWindows interface compiles, but is completely broken. I'm afraid it
needs a full rewrite (to support the various game modes in particular).
