Negamax with alpha-beta on Position scores every move; the strength sets the
depth, the softmax temperature and the chance of a random move. The levels
are ranges of strengths drawn per game. A calibration tournament checks that
each level beats the one below.
Position keeps the board as 14 stone counts and plays the Mangala rules on
it without allocating. Tested against MancalaGame with the recorded games and
random games.
