Add an option to the UPnP database plugin to configure which interface
is used by upnp to discover servers.

upnp by default selects the first interface that is not loopback, which
in some cases might not be the desired interface. For example if wanting
to access a DLNA server over a VPN connection.

The "interface" option can now be set to the name of the desired
interface to achieve this.

The default behaviour remains unchanged.

Closes https://github.com/MusicPlayerDaemon/MPD/issues/1297

This reduces duplicates in the music database by hiding the original
song file when it is referenced by a CUE sheet.

Closes https://github.com/MusicPlayerDaemon/MPD/issues/1275

The implementation was removed 12 years ago in commit f6455d5f and
nobody missed it.

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.

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.

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

Very rough draft.  Barely works.

New experimental code, first draft - it works, but there's a lot left
to do.  Just look at all the TODO comments.

Closes https://github.com/MusicPlayerDaemon/MPD/issues/975

Add cacert option for curl plugin

    add cacert option for Curl plugin. Allows to set cacert for curl lib
    Added documentation line into doc/plugins.rst with explanation for cacert option

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

MPD uses soxr with prefined resample recipes. Soxr also support defining a recipe your self.
This commit will support a custom recipe by changing the existing quality setting to "custom".

The same structs as the predefined recipes uses can now set by hand.

This will make the following settings available:
- precision 16|20|24|28|32 bits, example "28"
- phase_response - 0-100, example "45"
- passband_end - used bandwidth of source 80-99.7%, example "99.7.0"
- stopband_begin - anti aliasing 100.0+%, example "100".
- attenuation - signal reduciton in dB's, 0-30. example "3.0".
- flags "0" - additional bitmask with extra settings

The data is set in the structs soxr_quality_spec and soxr_io_spec (found in soxr.h).

Currently, the hardcoded URL points to a non-existent page.