Use std::string_view to avoid modifying the string for the temporary
null terminators.

release v0.21.22

Reduce I/O overhead.

Reduce I/O overhead.

The event library uses various libnet.a classes,
e.g. SocketDescriptor.

Move code from ParseCommandLine().

This method gets called a lot during MPD startup, via FindChild() and
directory_load_subdir(), so this is worth optimizing at the expense of
code readability.

This speeds up MPD startup by 10%.

This consumes more memory (plus 48 kB on 32 bit systems), but reduces
the number of hash collisions, speeding up MPD startup with large
databases.

This reverts commit eb192137.

This is no longer necessary because we require FFmpeg 3.1 or newer
since MPD 0.21.2.

This fixes a deprecation warning because the implicit AVPacket copy
constructor copies the deprecated attribute `convergence_duration`.

Enable lots of plugins for better CI coverage.

Was using the wrong parameter.