20200612 minesweeper clone

Today's effort is a minesweeper clone, written in Java. This uses tty magic to
clear the screen, so probably won't work on Windows.


I feel strong satisfaction at having gone from nothing to a working github
project within a day.

The model of square enumeration I have chosen is rough and ready. Each
possible square state is represented by a byte value.

In retrospect, it would have been better to use bitmasking. Consider if each
square would be represented by a byte of this structure,

    Low five bits:      Number of neighbouring squares containing bombs (less
                        than or equal to 8)

    High three bits::   is_bomb | is_marked | is_revealed

The code required to work that structure would be tighter than today's effort.
It has been four years since I attempted anything in Java, and far longer
since I build anything that worked. Result.