This eliminates some overhead, because the compiler doesn't need to
consider these functions throwing.

We'll have some code for it soon.

Prepare for DSD sample rate fixups.

This new library is integrated in the PcmExport class and (if enabled)
converts MPD's channel order (= FLAC channel order) to ALSA channel
order.

This fixes:
 http://bugs.musicpd.org/view.php?id=3147
and
 http://bugs.musicpd.org/view.php?id=3255

The standard has been renamed since the early draft that was
implemented in MPD.

Move code from the ALSA output plugin.

For 32 bit DSD-over-USB support.

Prepare for removing SAMPLE_FORMAT_DSD_OVER_USB.

Converts padded 24 bit samples to packed 24 bit samples.  Will replace
the packed S24 sample format, which is not used internally.

Delete the now-unused pcm_byteswap library, and optimize the
pcm_export_state object.