Add function to find winning position
Add winning and defensive move strategies
Generalize the 'find-winning-position' function

This function will now look for a row that hasn't been filled yet by the
other opponent but has a slot taken by the specified opponent. You can
tell it how many slots should have already been taken.
Add offensive move

This will look for rows where we've taken one spot and there are two
other free
Be consistent with using T (uppercase)