Replaced the mileage information by a score
The score depends of the player's speed
Added a class to load and save best scores using json
Added the implementation of ScoreManager::getRank(int)
Added a new game state : the "new record game state"
It allow a user to type its pseudo and see the top 10 players
The user can now quit the game in all states by pressing the escape key
Removed the frame rate limitation since the race animation seems to be smoother
Changed the GameState system to make it easier to use