default_value defaults to nullptr.

Drop support for misencoded tags.  People should not be using ID3v1
anyway.

Build a table of pre-existing tag types before adding new items.  The
old way would check HasType() each time, which would return true after
the first instance of that tag type had been added, preventing
duplicate tag types to be merged.

This broke duplicate tag types loaded from the state file, because
this code path uses TagBuilder::Complement().

New in clang 3.6.

This was used by proprietary software.  MPD adopted it a few years
ago, which turns out to be a mistake, because it now creates problems
for some MPD users (http://bugs.musicpd.org/view.php?id=4168).

On "list albumartist", songs that have no AlbumArtist tag will use the
Artist tag.  However, if AlbumArtist is disabled via
"metadata_to_use", the TagBuilder::AddItem() call is ignored, and
PrintUniqueTag() attempts to print a nullptr string.

This commit fixes the problem by attempting the fallback only if
AlbumArtist is not disabled.

Fixes buffer overflow bug.

Fixes buffer overflow bug.

MPD handles all strings in UTF-8 internally.  Those decoders which
read Latin-1 tags are supposed to implement the conversion, instead of
passing Latin-1 to TagBuilder::AddItem().  FixTagString() is simply
the wrong place to do that, and hard-coding Latin-1 is kind of
arbitrary.

The new tag is supported by all decoders that use the tag name table,
and the ID3v2 tag "TSOA" maps to it.

The Release Track Id uniquely identifies a recording on a release - that
is, even if a recording appears twice on a release (meaning that the
combination of recording and release id are not enough to figure out
which one it is), the release track id will allow differentiating the two.

The tag names are taken from
https://musicbrainz.org/doc/MusicBrainz_Picard/Tags/Mapping

Move code from the Vorbis and FLAC decoder plugins.

Enables using range-based "for".