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!

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

... and switch from debug build to release

...on Android

Moved all external libraries used by raylib to external folder inside
raylib src. Makefile has already been update and also the different
includes in raylib modules.

Android build system has been simplified and now is included in src
folder, like other build systems.