Closes https://github.com/MusicPlayerDaemon/MPD/issues/1337

Closes https://github.com/MusicPlayerDaemon/MPD/issues/1328

Closes https://github.com/MusicPlayerDaemon/MPD/issues/1106

Closes https://github.com/MusicPlayerDaemon/MPD/issues/1285

This commit also increases the PROTOCOL_VERSION so clients can detect
the availability of the feature.

Whoops, I misplaced this one.

Another one from https://github.com/MusicPlayerDaemon/MPD/issues/888

Closes https://github.com/MusicPlayerDaemon/MPD/issues/888

The existing implementation has been utterly broken forever; I cannot
explain what it actually does, but it doesn't do what the
documentation says.

Now, "+0" means "right after the current song" and "-0" means "right
before the current song".  Mnemonic: there are zero songs between the
current song and the newly added song.

A similar feature was present long ago in MPD, but was deprecated in
version 0.16 because the implementation was broken.  This commit
re-adds the feature in a way that's well-defined and not broken.

Close https://github.com/MusicPlayerDaemon/MPD/issues/1221

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".

Exmaple -> Example

Closes https://github.com/MusicPlayerDaemon/MPD/issues/1022

Increasing the protocol version to 0.22.4 to allow clients to detect
this feature.

Closes https://github.com/MusicPlayerDaemon/MPD/issues/1038

The `{TAG} {NEEDLE}` input format documented seems to be a holdover
of pre-0.21 filters, and the commands support the new format.

Closes https://github.com/MusicPlayerDaemon/MPD/issues/979

And un-deprecate "pause" without parameter (toggles pause).  I have no
idea why it was deprecated long ago; the deprecation notice was copied
from the ancient MPD wiki.

Closes https://github.com/MusicPlayerDaemon/MPD/issues/944

Closes https://github.com/MusicPlayerDaemon/MPD/issues/893

The parser implemented in libmpdclient requires the first key-value pair
of the server response to be the file pair. This is due to the fact that
libmpdclient scan pairs sequentially and first attempts to extract the
file pair before parsing the currentsong response further. See:

	https://github.com/MusicPlayerDaemon/libmpdclient/blob/5c751a761ec9f71a43ee0e41cfff3208f31a58b8/src/song.c#L559-L563

Meta data encoded as pairs in the currentsong response will be ignored
if they are placed before the file pair in the response.