Fix Makefile files

I've added .PHONY targets and fixed "clean" recipe.

Only defaultShader required, set default value for vertex color
attribute if not enabled and fragColor uniform

Cleaning of Makefile files

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

if mesh is not loaded properly it breaks the game!

Fix spacing and some comments

Physac redesign complete

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.

...despite not being enabled on GLFW3

Redesigned to work as standalone and support fordward-compatible context
(shaders review)

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.

Now it works ok also in RaspberryPi

physac module redesign (2/3)

physac module base almost finished. All collisions are now resolved
properly and some force functions was added.

COLLIDER_CAPSULE removed for now because in 2D everything is composed by
rectangle and circle colliders...

The last step is move physics update loop into another thread and update
it in a fixed time step based on fps.

Fix examples and templates compiling on GNU/Linux

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>.