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.