* explained a bit more the core_window_letterbox example

* fixed a few 'ups' moments that could lead to mild head pain and time loss

The result of `success` is actually never used. Either we should check
for it and return or remove it. I assume just checking the last one is
okay.

Replaced DEPRECATED functions

...moved to internal AudioBuffer structure as totalFramesProcessed, now time measure works again... but there is some problem with looping...
Also note some inconsistencies between frames and samples, it seems those concepts are not considered correctly in the code.

All data should be properly initialized by now

Renamed for consistency with similar functions

Now, multiple music parameters are exposed to the user!

This module has been completely reviewed, old structures still contained OpenAL useless data, a full module revision. Some of the changes:
 - Redesigned internal MusicData structure
 - Exposed MusicStream structure data
 - Reviewed AudioStream structure
 - Redesigned Sound structure

Still some work to do...

- Capital letters at beginning
- for loop spacing and brackets
- Functions naming for consistency
- Example following examples template
- Other tweaks

* added multi channel sound replay to raudio
added -fPIC to Makefile for Linux
added simple lighting and audio multi channel to examples Makefile

* not properly reporting audio buffer pool size...

Users can define their custom memory management macros.

NOTE: Most external libraries support custom macros in the same way, raylib should redefine those macros to raylib ones, to unify custom memory loading. That redefinition is only implemented as example for stb_image.h in [textures] module.

It seems individual sound volume level is not set...

Reported on rfxgen tool, it crashes on some parameters

raudio AudioBuffer internal struct collides on macOS with CoreAudio same name struct. In this case struct has been renamed because is internal to raudio... but probably all system should be redesigned.

Planning to promote raudio module as a simple and easy-to-use front-end for the amazing mini_al library, so the name change.

Name comes from raylib-audio but in spanish it also remembers to word "raudo", meaning  "very fast", an analogy that fits perfectly to the usefulness and performance of the library!

Consequently, raylib version has been bumped to 2.4-dev.

Despite issue is corrected, now module loop doesn't work...

Useful in case raylib compilation want to be automated and compilation config flags provided by command line.