no practical difference, just the compiler being annoying on linux

see GitHub issue #1

This adds the internal management of the seeking, as well as the decoder backends bits.

makes the player process optionally send back a string describing the failure to provide a better and more coincise error message. This turns the syslog message(s): amused: unknown file type amused: failed to play, skipping /home/op/pics/phos.jpg into: amused: unknown file type; skipping /home/op/pics/phos.jpg

the API is a bit of a shitshow. op_fdopen is just a wrapper around FILE*, but returns void* for don't know what Windows limitation. if op_open_callbacks fails we have to free the stream by ourselves. the documentation implies that this void* pointer is, in fact, a FILE*.

when the function was renamed, the error messages weren't.

i am just unable to do a proper refactoring. When i changed the return type of play_opus I mixed `r' and `ret', so it would always play zero samples...

this will allow to remove the `got_stop' hack in player.c

with the recent refactoring, sndio is only visible in player.c