The goal is to eliminate all balls in the board. The game will be end if there
is no more ball (You Win), or if there is no more possibility to eliminate
them (You lose). Ball will be eliminated if there are more than one ball at
horizontal or vertical direction. Non-ball object is movable, but it is not
able (and it is not the goal) to eliminate them.
For every level, there is a maximum number of step. Game will be end (and you will lose) after this number of step.