Correcting details that pop-up when testing the different platforms

raylib uses spaces between '+' and '-' signs but not between '*' and '/'
signs, it's a chosen convention

- LoadWave()
- LoadWaveEx()
- UnloadWave()
- WaveFormat()
- WaveCopy()
- WaveCrop()
- GetWaveData()

Simplified module for Music and AudioStream
Added support for raw audio streaming (with example)

Still some work left...

Some review work still required...

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

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.

Moved AudioError enum inside audio.c

The only thing I did not change was the _g for globals. Is there any
other way we can mark globals?

This is a first step toward a bigger project. Some modules could be
ported to header-only to be used as standalone.

_g naming convention for globals, new error exit numbers.