Powerups, Boat Speedup and Bugfixes

Health powerup implemented.
Crate particle effect added.
Boat can now speed up and slow down with W and S.
Inventory updated with points for each item, total points, and distance
travelled.
Bugfixes for sections including the fixing of overlapping lakes after
split sections, sections spawning an entire section too far back or
forward, and rock distribution has been fixed so it no longer is biased
towards the right hand side of the section.
Crocodile clipping with boat has been fixed.