Ball physics change

I changed the physics of the ball bouncing off the racquet to give the player more control and to vary the game play. The result is that the racquet behaves as if it is curved so you can direct the ball in the x direction.

I had to change the ball variables from ints to doubles. I also altered the code for bouncing off the walls to retain magnitude of velocity. This is quite a major change to the play of the game so let me know if it isnt the direction you want to go.

Note: I haven't updated the executable so it still runs the old game.