Connect4 eval function

[oggy22]

Write a good eval function for Connect4 with the following properties:

• Return max if there is a winning move.
• Return min if there are two winning moves for opponent if it was their turn.
• Treat each column independently. Their order doesn't matter as well.
• For each player and for each empty field identify if it's a missing 4th
• Double (winning) chance should have high score
• If a field is a missing 4th for both players, the fields above are ignored. This is because they will be never played on as the player who plays on the missing 4th will win.