Audio modding support

This might have been suggested before, but it would be great to see some audio mod support in FiveReborn since the mods folder seems to not work anymore. I think it’d be great for people to use their engine sound mods, police sirens and such in FiveReborn.
If this was suggested before… well, sorry?

@NotGigo it would also be good to get audio functions for audio files in a local directory.