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

The model for enumerating squares is rough-and-ready. Each possible square
state is represented by a byte value.

In retrospect, it would have been tighter 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.