Piece has four possible values: X,O,Invalid, and Blank
Piece board[BOARDSIZE][BOARDSIZE]
board represents the 2D playing board, where BOARDSIZE is 3,
Piece turn
turn represents whose turn it is to place a piece (defaults to X)
TicTacToeBoard()
Constructor sets an empty board and specifies it is X's turn first
Piece toggleTurn()
Switches turn member variable to represent whether it's X's or O's turn and returns whose turn it is
Piece placePiece(int row, int column)
Places the piece of the current turn on the board, returns what piece is placed, and toggles which Piece's turn it is. placePiece does NOT allow to place a piece in a location where there is already a piece. In that case, placePiece just returns what is already at that location. Out of bounds coordinates return the Piece Invalid value. When the game is over, no more pieces can be placed so attempting to place a piece should neither change the board nor change whose turn it is.
Piece getPiece(int row, int column)
Returns what piece is at the provided coordinates, or Blank if there are no pieces there, or Invalid if the coordinates are out of bounds
Piece getWinner()
Returns which Piece has won, if there is a winner, Invalid if the game is not over, or Blank if the board is filled and no one has won.