Minesweeper upgrade

I changed a bunch of stuff in the minesweeper game. The board is bigger, there's a smiley face that acts more like the original game, the tiles with no bombs next to them are now empty instead of displaying a "0", etc. There are also some preparations for having customizable board sizes (or at least a couple of options), and variable mine counts. I've also updated the HEX and ELF files, and added a new (but crappy since I can't run the emulator) picture.

EDIT: I've also changed the way tile uncovering works. A detailed description of the change is in my [commit message](https://github.com/qubist/Gamebuino-Minesweeper/commit/18c7862744321a8bcfc4bd6def8404ca29211486)