Provides summarized data representing a player's board in a puzzle game. Board summaries are maintained by the puzzle server and are periodically sent to the clients to give them a view into how well their opponent(s) are doing. The data required to marshal a board summary object should be notably smaller in size than what would be required to marshal the entire associated {@link Board}.
Note all non-transient members of this and derived classes will automatically be serialized when the summary is sent over the wire.