"""
Tic Tac Toe board game
    - Human vs. computer player
    - Human plays first
    - Computer always plays valid moves

Command-driven UI !!!???
    play 1,1  # (1,1) is center square on the 3x3 board
    takeback  # takes back human player's last move
    ragequit

What to look out for today:
    1. Modular programming
    2. Test-Driven Development (first examples)
    3. Using Exceptions
"""