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.

These have no use, exception for creating an artificial dependency
from input_plugins[] to all archive plugins.

Simplify the definition of many build options.

I've created an elementary input plugin that plays sound from the
soundcard, so you can use MPD to listen to anything connected to the
line-in jack, or to Video4Linux FM radio cards that send audio through
the soundcard.  There has been a small number of posts here in the
past requesting line-in input, so here is a first, simplistic stab at
it.

The patch adds a new sheme, alsa://, which causes mpd to play data
read directly from a souncdard.  It defaults to hw:0,0, but you can
pass any ALSA device name in the URI.  So, using mpc for example:

 mpc add alsa://
 mpc play

will play from device hw:0,0.

To use a diffferent device:

 mpc add alsa://hw:1,0

This plugin is cumbersome to support, now that MPD is migrating away
from GLib and the GLib event loop.  It has no practical advantages
over the CURL plugin.  Soup requires the bloated GType library.

To demonstrate the new I/O thread.  libsoup is well-integrated into
the GLib main loop, which made this plugin pretty easy to write.

As a side effect, we have to initialize the I/O thread in all debug
programs that use the input API.

For Spotify tracks. Uses a spt URI, so with mpc you can play tracks
with e.g.,

  mpc add spt://spotify:track:5qENVY0YEdZ7fiuOax70x1
  mpc play

Uses the pcm_decoder_plugin for the output

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.

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.

If a feature is disabled, don't compile the source file at all,
disable it completely in Makefile.am instead.

Yet another patch which converts pointer arguments to "const".

The ID3 code uses only the public tag API, but is otherwise
unrelated.  Move it to a separate source file.