`HOST_NAME_MAX` is not a portable macro; it is undefined on some
systems.

Closes #402

std::regex_replace() is heavily bloated and overkill for this feature.

expand %h to the system hostname and default to a zeroconf string that
contains %h

So long, autotools!  This is my last MPD related project to migrate
away from it.  It has its strengths, but also very obvious weaknesses
and weirdnesses.  Today, many of its quirks are not needed anymore,
and are cumbersome and slow.  Now welcome our new Meson overlords!

Calling dbus_shutdown() too early will break the "udisks2" neighbor
plugin.

Fixes Mac build failure.

This flag is never read.

Make valgrind happy.