During the libfmt migration, I converted "%1.3f" to just "{:1.3}"
without the "f" suffix, but libfmt defaults to scientific notation,
which can break some MPD clients.

Closes https://github.com/MusicPlayerDaemon/MPD/issues/1291

Fixes protocol breakage after commit 0440c41c

libfmt is too clever for the MPD protocol!

Closes https://github.com/MusicPlayerDaemon/MPD/issues/1175

Found with -Wdouble-promotion
Signed-off-by: Rosen Penev <rosenp@gmail.com>

Found with readability-uppercase-literal-suffix
Signed-off-by: Rosen Penev <rosenp@gmail.com>

This is the case with uClibc-ng currently.
Signed-off-by: Rosen Penev <rosenp@gmail.com>
(cherry picked from commit 769cd0ee9f0cf8ceb026aa751b5d4a390bb5dbdc)
(changed define to match master)

Found with -Wdouble-promotion
Signed-off-by: Rosen Penev <rosenp@gmail.com>

[[maybe_unused]] (introduced in C++17) is standard C++.

https://clang.llvm.org/docs/AttributeReference.html#maybe-unused-unused
says that this is equivalent to the GNU unused attribute.
Signed-off-by: Rosen Penev <rosenp@gmail.com>

This is the case with uClibc-ng currently.
Signed-off-by: Rosen Penev <rosenp@gmail.com>

Found with readability-uppercase-literal-suffix
Signed-off-by: Rosen Penev <rosenp@gmail.com>

The "-1" magic value is deprecated now.

Prepare to convert "partition" to a mutable pointer.

This code (added 7 years ago with commit b233c145) has been obsoleted
by the SongLoader class (added 3 years ago).

Move code from ReplayGainConfig.cxx.

Move code from replay_gain_get_real_mode().

Prepare full C++ exception support in the player thread.

Prepare for moving idle events to class Partition.  Right now, it's
just a wrapper for idle_add().