more complexity to refactor. including a UI (console) to make testable

This codebase, is a starting point for a refactoring-kata. When you get tired from the simple ones, try and make this code, and especially the UI, so that the 'console-style' doesn't leak through the whole UI.

extra 'features' to add :

• make the system detect that a player has won, and ask for a new game;
• make the system aware of more tennis context and
  • make it behave as a set of 6 games
  • make it aware of winning a set only if you win by 2 setpoints
  • ... well you get the point