Javadocs + Small GameStats changes.

-Added javadocs to Card.java - toString()
-Added javadocs to Game.java - concludeGame()
-Added javadocs to GameStats.java for every method/class.
-Changed javadocs in Main.java.
-Changed formatting of some of the game stats, properly handles 0 rounds
played.
-Change getDurationString in RoundStats to getDuration.
-Added entire game duration to game stats.