Acceleration is not a persistent part of the PhysicsState, and is only used for intermediate calculations along a trajectory.
Fixes several bugs:
- Walk decelerate clip into wall
- Walk accelerate clip into wall
- Fall while flying
Reviewed-on: #30
Co-authored-by: Rhys Lloyd <krakow20@gmail.com>
Co-committed-by: Rhys Lloyd <krakow20@gmail.com>