Added a timer class which checks whether a certain duration of time has elapsed since it last reset.

I then used this class in the Game class to create a constant, predictable fps, right now it runs at about 81-84.
Changed the default ball velocity to {0, -12} and initialized it inline instead of introducing an unnecessary local variable.

Also made another one of those cool ASCII arrow things to document the inline velocity.
Moved the double slashes to the correct indentation level. So it's consistent.