This is an elisp implementation of the classical minesweeper game.
The target is localize all hidden mines (bombs) in a rectangular board
without detonating them.  You reveal the content of a cell with the
command `mines-dig'.

1. Cells with a bomb contain the character 'x'; if you call `mines-dig'
   in these cells then you lost the game.

2. Cells without bomb at distance 1 from any cell with a mine
   contain a number: the number of bombs at distance 1 from this cell.
   If you reveal the content of this cell, then this number is shown.

3. Cells without a bomb at distance > 1 from any bomb contain '@'.
   If you reveal the content of this cell, then '@' is shown and
   all adjacent cells are recursively revealed.


If you think that an uncovered cell has a mine, you might flag it
with `mines-flag-cell'; if you call this command again in the same
cell the cell is unflagged.  This is useful to visualize your
progress in the game.

The game is completed once all mine-free cells are revealed, that is,
when the only uncovered cells equals the number of hidden mines.