Added a Pity Boost Feature

Find yourself falling behind in this epic racing battle?  We added a mechanic just for you!  Now, if you are the last player to pass a checkpoint, then you'll receive a boost to help you keep up with the other players in the race.

The checkpoints that give you these boosts are still invisible.  If we decide to keep the pity boost, we'll need to make those visible later in development so you the player can see what's causing the boost.