Duidoku: The two-person Sudoku game

Rules:
Pick a square grid size (any of 4, 9 or 16. Editing line 22 will allow for more square grid sizes)

Player A starts, inputting a move in the form: row, column, value
Row and Column range from 0 to (grid_size - 1)
Value ranges from 1 to grid_size

At any point in time, input s to save game state, l to load game state, and q to quit
Don't worry about losing your place when saving/loading, the program knows whose turn it is

Keep going until a player can't make a valid move. That player loses, and the other player wins!

If all possible spaces are occupied, it's a tie