See also https://github.com/MusicPlayerDaemon/MPD/issues/1061

Closes https://github.com/MusicPlayerDaemon/MPD/issues/1570

Closes https://github.com/MusicPlayerDaemon/MPD/issues/1532

`playlist_plugin` blocks use `name` to identify the plugins.

The writing and reading of metadata involves lots of different programs
and libraries. Therefore it is prudent to point out how exactly MPD
receives metadata. Ideally this helps to point users to the right place
if their tags are not picked up correctly.

Closes https://github.com/MusicPlayerDaemon/MPD/issues/1115

Some users want certain clients to fully control playback, but do not
want them to be able to trigger database update.

Closes https://github.com/MusicPlayerDaemon/MPD/issues/1124

I want to use per-subproject warning_level (0.56.0), default_library
(0.54.0).

NB: Check the sysconfdir setting to determine where mpd will look for mpd.conf; if you expect mpd to look for /etc/mpd.conf the sysconfdir must be '/etc' (i.e., not 'etc' which will result in mpd looking for /usr/local/etc/mpd.conf):
 
.. code-block:: none
 
 meson configure output/release |grep sysconfdir

If this is not /etc (or another path you wish to specify):

.. code-block:: none

 $ meson configure output/release -Dsysconfdir='/etc' ; meson configure output/release |grep syscon
  sysconfdir              /etc                                               Sysconf data directory

Updating the database no longer requires the `admin` permission, only
`control` is needed (changed in 2abad0f4).

See also: #1124

Closes https://github.com/MusicPlayerDaemon/MPD/issues/1112

This allows users to disable the "CUE files as directories" feature
without having to disable the CUE playlist plugin completely.  This
feature has been annoying some users.

The bug https://bugzilla.samba.org/show_bug.cgi?id=11413 makes MPD
crash after at most a minute of using the plugin.  Since this bug is
five years old already and it doesn't look like it will ever be fixed,
all libsmbclient code in MPD is scheduled for removal.  For now, the
plugin is disabled by default so people are less likely to hit the
crash bug.

Closes https://github.com/MusicPlayerDaemon/MPD/issues/991

--stdout was renamed to --stderr in 72617395.

Commit 60f957ed broken the GCC 7 build, but instead of working
around missing C++17 features in old compilers, let's update the
compiler version requirements.

This commit raises the clang requirement to version 5 because this is
the first version to support `constexpr` lambdas, to be used to
`Dsd2Pcm.cxx`.