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.