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

While this assert() was useful when we had to track the object's state
manually, there was no practical purpose other than verifying old
code, and it complicates our new C++ code.

Instead of just adding a rectangular random value before shifting back
to the normal scale, use the existing PcmDither library.

Prepare for adding state.

Remove GLib dependency from some headers.

The other audio_format attributes are not used.

This updates the copyright header to all be the same, which is
pretty much an update of where to mail request for a copy of the GPL
and the years of the MPD project. This also puts all committers under
'The Music Player Project' umbrella. These entries should go
individually in the AUTHORS file, for consistancy.

Don't abort MPD when a sample format is not supported by pcm_volume().

1024 is 2^10, and allows gcc to use bit shift operations instead of
multiplication / division.

In generic PCM functions allowing all sample formats, pass a void
pointer instead of a char pointer.

Moved the software volume code to a separate library.

Don't use libc's rand() function, because it is slow.  Our own trivial
linear congruential generator is good enough for dithering.

redirect_stdin() is a daemonization function, and disconnecting from
the standard input is always a good idea for MPD.

Prepare for the migration to the GLib option parser, which uses
gboolean for flags.