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

Explanation

This adds support for DOP using the PcmExport function if the macro
ENABLE_DSD is defined. If enabled within the config-file using "dop",
the boolean dop_setting will be true. If DSD input is encountered and
the setting is on, it is checked whether the oss-device supports the
required samplerate. If that is the case, dop_active is set to true
and conversion of the input is prevented. If the sample rate is not
supported, conversion to S32 is requested. When playing back, the
PcmExport is used to pack the incoming stream into PCM.  Reasoning

This is required for OSs without the required driver support for
native DSD playback that also have no ALSA. Mainly *BSD users are the
target audience for this functionality, as ALSA here is only a proxy
without full functionality.  Requirements

    DAC that supports the DOP standard
    Building with OSS, DSD and S32-Format

Supported Formats / Required PCM Formats

DSF, DFF and WavPack-DSD will work.

DSD64, 1 Channel -> S24:176.4kHz (untested, lack of time / missing samples)
DSD64, 2 Channel -> S24:352.8kHz
DSD64, 4 Channel -> S24:705.6kHz (untested, lmissing equipment)
DSD128, 1 Channel -> S24:352.8kHz (untested, lack of time / missing samples)
DSD128, 2 Channel -> S24:705.6kHz
DSD256, 1 Channel -> S24:705.6kHz (untested, lack of time / missing samples)
Changes

    inclusion of required files
    adding new domain for logging
    adding dop_satisfied private function
    adding required member variables for storing dop state and for dop-packing
    adding dop boolean parameter to many functions that are required to act a little differently when dop is active

Testing

This has been tested to work with a Sabaj Da2 on FreeBSD, where the
red status indicator LED clearly shows that DSD playback is taking
place, instead of purple for "hi-res" which is seen when converting.
Issues

I have not tested this with S24 and right now AFMT_S32_NE is
required. If not defined, ENABLE_DSD will be undef'ed. This will be
addressed in a bit, however no DAC which supports DOP but not 32Bit is
known to me. Also, AFMT_S32_NE is not defined when building on FreeBSD
which is why this is just blatantly defined in the file at the moment.
Additionally, the new dop-option is not added into any documentation
whatsoever.

This plugin has been defunct for several years.  Tidal has not ever
replied to any of my emails, so they're apparently not interested in
MPD support.

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

See also: #1124

Since we migrated to readthedocs.io, we don't need this target
anymore.  And Meson 0.58.0 apparently has a change breaking this
target.

Closes https://github.com/MusicPlayerDaemon/MPD/issues/1161

refactors GenerateOggSerial into a generic GenerateSerial
utility, under the util lib.

libFLAC may be encoded without Ogg support. If Ogg support is disabled,
libFLAC will still export Ogg-related methods (like setting a serial
number), and throw a runtime error when initializing an Ogg stream.

GenerateOggSerial does not depend on libogg. Refactoring it into
a generic GenerateSerial prevents having to add build-time checks
for libogg within the FLAC encoder plugin.

This enables the JACK output plugin on Windows, but doesn't link
against libjack64.dll, instead loads the DLL at runtime with
LoadLibrary().  This kludge avoids the extremely fragile JACK shared
memory protocol by using the system's libjack64.dll, without requiring
the same DLL at build time.

This commit adds some tags that are (mostly) interesting for listeners
of classical music.

Ensemble
--------
This is an ensemble that is playing the music, such as Wiener
Philharmoniker. The tag can be used to distinguish the ensemble from the
conductor, composer, soloist, and ensemble, that are generally all in
the "ARTIST" tag.

Movement
-------
The movement number and movement (name) of this track, i.e.  "II" and
"Allegro".

ComposerSort
------------
Allows us to look for Beethoven's 9th under B, for Beethoven, not L for
Ludwig.

Location
--------
This is the location of the recording, e.g. "Wiener Musikverein".

Closes https://github.com/MusicPlayerDaemon/MPD/issues/1102

Very rough draft.  Barely works.

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

At least I believe libmpdclient is reading env. var. as second:
https://github.com/MusicPlayerDaemon/libmpdclient/blob/master/src/settings.c#L142

ncmpc manual also mentions MPD_TIMEOUT being is second.