move2String function
- int x
 
Convert playerd square to human readable String.
e.g. f5
Implementation
String move2String(final int x) {
  if (0 <= x && x < boardSize) return _moveStringTable[x];
  if (x == MoveMark.pass) return 'pass';
  if (x == MoveMark.noMove) return 'no move';
  return '';
}