Fixes build failure on Debian Wheezy.

Use the snd_pcm_t only in the IOThread, and reuse code that is
well-known to work.

Comes with a callback pointer instead of a virtual method, which
allows multiple instances in one class.

Replaces the old BoundMethod template.

release v0.19.16

Previously the id was being returned only when a position wasn't
specified.

.. instead of doing it after seeking.  After seeking, the command had
no effect, because CheckDecoderStartup() waits for all outputs to
finish.  This caused a very long delay while seeking and switching
songs (https://bugs.musicpd.org/view.php?id=4534).

Signed-off-by: Lazaros Koromilas <lostd@2f30.org>

Signed-off-by: Lazaros Koromilas <lostd@2f30.org>

https://bugs.musicpd.org/view.php?id=4525

Use libvorbis instead of libvorbisfile, which gives us more control
over the decoding process.

This reverts commit 995cd954.  It was
a bad idea because it caused assertion failures when a decoder plugin
aborted with an exception.