might help with portability, see for e.g. GitHub issue #1

we're just gonna memcpy all over path again a couple of lines before; a smart compiler will probably ignore the initialization anyway.

was the only function to disrespect the player_* namespace (well, excepting play). while here also don't mark those two as static, they were the only static functions in the file. I'm not trying to enforcing private symbols here.

we don't know what format the music will be so we have to stop and set the parameters in player_setup. there's no point in setting bogus parameter in audio_init.

don't need to keep `files' around, res->files is enough. it would have prevented the previous bug (probably.)

don't advance the files pointer, we need the original pointer when receiving the replies.

the approach with one-function-per-imsg leads to too much code splatted across the file.