Server: Filter non-audio files in libav music_tag implementation.

Signed-off-by: Peter Tworek <tworaz666@gmail.com>
Server: Rework main loop to use libevent and add scheduler subsystem.

The task/event scheduler is supposed to be a simple way to execute
handle multiple long running tasks in parallel on a predefined nuber
of threads. The code is not used right now, but will be in audio
converter module.

The task scheduler also provides a simple way to register an immediate
callback function executed directly from the main event loop.

Signed-off-by: Peter Tworek <tworaz666@gmail.com>
Server: Make the code compile with -ansi compiler flag.

Signed-off-by: Peter Tworek <tworaz666@gmail.com>
Server: Integrate logging subsystem with libav and libevent.

Signed-off-by: Peter Tworek <tworaz666@gmail.com>
Server: Initialize logger in scheduler-test.

Signed-off-by: Peter Tworek <tworaz666@gmail.com>
Scheduler: Make sure cancel callback is invoked when terminating.

Signed-off-by: Peter Tworek <tworaz666@gmail.com>
webserver: Fix compilation warning.

Signed-off-by: Peter Tworek <tworaz666@gmail.com>
music_db: Log adding file to database in debug category.

Signed-off-by: Peter Tworek <tworaz666@gmail.com>