New refactoring example code

Tennis game - display score for tennis game
1. 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.
2. The running score of each game is described in a manner peculiar to
tennis: scores from zero to three points are described as "love",
"fifteen", "thirty", and "forty" respectively.
3. If at least three points have been scored by each player, and the
scores are equal, the score is "deuce".
4. 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.