NOTE: It requires a depth texture as input, it should be configured on
rlgl, by default RenderTexture (fbo) uses Depth Renderbuffer instead of
Depth Texture. Check rlglLoadRenderTexture()

Now it's possible to render to texture, old postprocessing system will
be removed on next raylib version.

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.

Depth test disabled for 2D and only used on 3D; consequently LINES vs
TRIANGLES vs QUADS buffers drawing order maters... but blending also
works ok.

I've renamed all makefile files to "Makefile" because they appear in the first files.

I've added "-ldl" library, it's necessary to compile the project.

I've cleaned the GNU/Linux compilation, now you can compile without useless parameters.

If you have raylib on standard directories ("/usr/local/include/raylib/raylib.h" for the header and "/usr/local/lib/libraylib.a" for raylib library) you can compile without edit the makefile.

I've changed all default target names with 'all'. Here there is the explanation: <https://www.gnu.org/prep/standards/standards.html#Standard-Targets>.

physac modules is being redesigned. Physics base behaviour is done and
it is composed by three steps: apply physics, resolve collisions and fix
overlapping.

A basic example is currently in progress. The next steps are try to add
torque and unoriented physic collisions and implement physics basic
functions to add forces. Rigidbody grounding state is automatically
calculated and has a perfect result. Rigidbodies interacts well with
each others.

To achieve physics accuracy, UpdatePhysics() is called a number of times
per frame. In a future, it should be changed to another thread and call
it without any target frame restriction.

Basic physics example has been redone (not finished) using the new
module functions. Forces examples will be redone so I removed it from
branch.

A deeper revision required, not clear enough for the user
Key: Create a PhysicObjects pool

- Added function WorldToScreen(...).
- Added world to screen example.
- Review GetMouseRay() comment.
- Removed deprecated lighting functions from raylib header.