show returns whether a bomb has been uncovered.
Colours are now cribbed from a screenshot.
Several updates.

Added #reset_game to restart the game.
Added start time.
The chord action is now initiated.
Updated drawing. Mark only flips if closed.
Total re-factor to correct everything.

The biggest problem (wraparound left <=> right) fixed.
open_all shows all blocks.
Added GridPos class to convert (row, col) <=> Index.
neighbours returns correct neighbours now (no WR-L)
Added debug option: Press O to open all.