Notable changes:
* IsSourcePlayingSomething had undefined behavior when checking unattached and unpositioned sounds.
* loading Blood RAW sounds with different sample rates but the same backing lump may not use the same hardware sound buffer.
* when playing an unpositioned sound the attenuation is irrelevant and must be ignored. This resulted in a 3D sound being started which was mostly inaudible due to lack of valid origin.
- added Marisa Kirisame's CHAN_OVERLAP flag.
- exported S_IsActorPlayingSomething to ZScript.
The sound API change required deprecating A_PlaySound and S_Sound. There are now new variants S_StartSound and A_StartSound which have two distinct parameters for channel and flags.
Also simplified the sound init decision making. With FMod gone there is no reason to be pedantic here. Even the check of snd_backend for the Null device could be omitted here, its only realistic use is '-nosound'.
Many of the simple wrappers have been moved to a separate file and the sound source handling has been abstracted.
This is only the first phase, the work is not complete yet.
Also changed the license of the sound code to BSD after verifying that this code bears no similarity to id's original sound code anymore, save for a few function names (which are due to be refactored out anyway.)
This implementation only reads GIF, BMP and PIC formats. No animated GIF support because stb_image does not handle that.
PNG, JPG and TGA are still being handled by the existing dedicated implementations.
PSD and HDR are impractical for reading texture data and thus are disabled.
PnM could be enabled, if its identification semantics were stronger. stb_image only checks the first two characters which simply would falsely identify several flats with the right colors in the first two bytes.
This is more or less a waste product of getting stb_image to work with something actually testable, so it is just provided as-is.
Now there is only one single entry point for both, instead of previously 2 entry and 4 exit points.
This also eliminates the explicit shutdown of ZMusic. Timidity++'s two buffers have been put in containers that self-destruct on shutdown and calling dumb_exit is not necessary because the only feature requiring it is not used by any code in the music library.
FMod had MP3/Ogg playback integrated right into itself, and the OpenAL backend tried to replicate this functionality.
This functionality, however, has been removed over two years ago when FMod started breaking things more and more, it was only this backing implementation that was left in.
This was the last player class.
This code was also cleaned up for non-Windows systems where CD Audio is not implemented.
Instead of providing an empty implementation, all related code is now explicitly deactivated.
It is now being handled by the controlling code.
While of no benefit for GZDoom itself, this finally allows to separate the entire music code into a separate, engine independent project that merely provides streamed music data when not playing on a hardware device (WinMM Midi or CD Audio.)
The tight coupling of the music code with the sound backend made this nearly impossible before
