Tweaks and cleanup

Tweaking the numbers used in the game, the weight of the ball, the
strength of gravity etc to make it more fun. Also cleaned up the code a
bit, removing commented sections with posX and posY instead of a pos
vector, removed some other old commented code snippets and unused
variables. Also fixed the way tennisBall is handled and the
createTEnnisBall function should now work as intended. Also cleaned up a
bit in the update function, making a separate checkEdges function to
handle bouncing with walls and within that function implemented min/max
y/x positions instead of manually writing those in the places they are
used to make it easier to for example add an area of the screen not in
used by the game.
Added features for tennisballs and multiple sounds

Added tennisball bouncing in inBall . Also added support for playing one
randomly selected out of multiple sounds for kicks and bounces (though
there is currently only one bounce sound). Oh and added playing sounds I
guess. Also changed the checkEdge method to take a ball instead of an
int so that it can check if it's a tennisball or a football and if the
former remove it, and if the latter die etc.
Adding tennisball

Currently in the process of adding tennisball. Currently there is no
purpose other than being another thing, and not yet tested if works but
added drawing, colission and destruction of a single tennisball. Can
relatively easily be modified to be a list. In  fact tha gives me an
idea to change the inBall feature to return a ball which could be null
if nothing is found?