Nice start, lots of room for improvement :

You are using 4 way flood fill, you could easily transform it into 8 way flood fill clear(cx+1,cy+1) and the like.

Chording support
game pad support
Mines remaining indicator (can be displayed in the corner furthest away from the mouse since the entire screen is occupied by the grid.
High score
Game restart (extcmd("reset") for example)
In game over screen, distinguish between flags, indiscovered bombs, incorrect flags and exploded mine.
Progressive reveal when hitting a 0.
...