Since we switched from autotools to Meson in commit
94592c14, we don't need to include
`config.h` early to properly enable large file support.  Meson passes
the required macros on the compiler command line instead of defining
them in `config.h`.

This means we can include `config.h` at any time, whenever we want to
check its macros, and there are no ordering constraints.

Will move attributes from struct AudioOutput that are specific to the
OutputThread.  The new struct AudioOutputControl is a holder for the
AudioOutput pointer.

This prepares for making the output list more dynamic, to allow moving
outputs to between partitions.

Another big chunk of code for multi-player support.

Replaces GLib's g_str_has_prefix().

Prepare to migrate away from GLib.  Currently, we're still using GLib
as a backend.

After we've been hit by Large File Support problems several times in
the past week (which only occur on 32 bit platforms, which I don't
have), this is yet another attempt to fix the issue.

If nothing has changed since the last save, don't save the state
file.  Saving will spin up the hard drive, which is undesirable on
hosts where MPD is idling in background.

Parse the state file line by line, let each subsystem probe a line.
Only the playlist_state code gets the FILE pointer to read the
following lines.

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 include output_api.h in output_internal.h.  This change requires
adding missing includes in several sources.

Moved code which deals with all audio outputs at once into a separate
library.