Implement a simple tennis game
Rules:
- Scores from zero to three points are described as “love”, “fifteen”, “thirty”, and “forty” respectively.
- If at least three points have been scored by each side and a player has one more point than his opponent, the score of the game is “advantage” for the player in the lead.
- If at least three points have been scored by each player, and the scores are equal, the score is “deuce”.
- A game is won by the first player to have won at least four points in total and at least two points more than the opponent.