Audio WIP on the rewrite:

* Introduce the audio API file that will be the new snd_public
Audio WIP on the rewrite:

* Ownerships changed a little between Sound and Emitter
* Emitters get a Sound to update instead of a Source (will be useful when we have shaders)
Audio WIP on the rewrite:

* Introduce loops back
* Remove most of the code in snd_openal.c so as to not have interferences