Finally, physics update is handled in main thread using steps to get
accuracy in collisions detection instead of moving it to a new thread.

Examples are finished as simple and clear as I could. Finally, physac
module is MORE simpler than in the first version, calculation everything
by the same way for both types of physic objects.

I tryed to add rotated physics a couple of times but I didn't get
anything good to get a base to improve it. Maybe for the next version...

No bugs or strange behaviours found during testing.

- Added new physics engine-module with four new data types: Physics,
Transform, Rigidbody and Collider. This library contains functions to
apply physics calculations to a position vector calculating collisions
automatically.

- Fixed some writing mistakes of lighting module.