*wip* encoder implementation

* transcode example
* make include/groove.h fit in 80 chars
* add groove_file_audio_format API
* GrooveSink: add disable_resample flag
encoder implementation compiling but not working
encoder: implement audio format fallback selection
transcode example working except the format header and trailer
encoder: implement headers and trailers (not working yet)
transcode example seems to be working

although the output file seems to not be very well formed