and remove static from PhysicsThread().

and add instructions in physac examples to run it successful.

and added PHYSAC_NO_THREADS define. Improved physac example drawing
frames per second in screen.

Required by gestures example....

Use instead: IsGestureDetected()

... and now physac thread creation is done in InitPhysics() and it is
destroyed in ClosePhysics(). User just need to call these functions to
use physac module.

This reverts commit 7999bbafa8.

Just started working on this, not sure if it would be available for
raylib 1.5

Old physics update system used a static number of steps to calculate
physics (450 for desktop and 64 for android). It was too much and it was
limited by target frame time...

Now physics update runs in a secondary thread using a fixed delta time
value to update steps. Collisions are perfectly detected and resolved
and performance has been improved so much.

To get it, use GetDefaultTexture()

AL/alext.h is not supported on html5 OpenAL implementation, just
replaced by the defines used in audio module

Only using raylib required extensions... it could be further reduced!

Adapted shaders for OpenGL ES 2.0

texture() doesn't exist in glsl 100, it must use texture2D().

Some shader calculations are now pre-calculated because some math
functions doesn't exist in glsl 110.

Fix Android template with 1.5 raylib features (audio streaming, gestures)