Fix #69
Reinstates the debug renderer in the rocket demo.
It is important to see the physics behing, as it seems the student like
this demo very much.
Removed unused class Vector2D
A possible semaphore class, maybe required
New facility methods for polygons
New PhysicsPolygon class which can contain arbitratly complex
shapes for physics simulation, given as a polygon.
Major camera bugs fixes
The camera was not updated for the `ShapeRenderer` in case of
translation of scrolling. This is now fixed. In addition, the
translation of the camera was now updated correctly. This is ok now.
Merge branch 'master' of https://github.com/pmudry/gdx2d

Conflicts:
	gdx2d-desktop/src/hevs/gdx2d/lib/physics/DebugRenderer.java