Add get/set squares, win checking, full board validation to Board.

+ Add Board.hasWin() to check board for winning rows, with
  corresponding Row.hasWin() method.
+ Add Board.isFull() to validate if all squares are full, with
  corresponding Row.isFull() method.
+ Add Board.fillSquare() and Board.fillSquareByCoordinate(), based
  on Row.fillSquare().
+ Add a "questions" file to track questions for Colin.