More structure (NOT YET TESTED!)

As it's stated in comments, there's no actual difference to the previous
version. However, we have a bit more structured code, in order to make
future features easier to apply:
- game_engine function: 0: tie, 1: player 1 wins, 2: player 2 wins
- getResultInStr: Returns the string to be printed to the user
With a few additions (for?) these funcs let us add more players and get
a little more flexible