New winning square algorithm

[dmorawetz]

@slovnicki asked for a cleaner algorithm to detect game termination.

Instead of comparing all the fields, we could track the state incrementally as described in this stackoverflow answer.

Basically, we keep an array of scores for every row, column and diagonal and update them after a valid move. Increment for X, decrement for O. When the score reaches 3 or -3 the corresponding player has won. We need such an array for every InnerGrid and one for the outer Grid.

[grayson-harrington]

It sounds like solving this issue will also solve the issue I created.

#36

[slovnicki]

It sounds like solving this issue will also solve the issue I created.

Not quite solve it, but definitely make it cleaner. Because we still need some higher canWin function.