This seems to work quite well including hotplugging of devices, changes to
default sinks/sources etc.
So far I only provided percentage values for sink/source since they seem most
useful. Defaults are set to DEFAULT_SINK/DEFAULT_SOURCE which means it will
follow whatever defaults are at the moment (instead of being fixed to a given
device).
One thing currently left unhandled is when pulseaudio/pipewire gets
disconnected/restarted. In such a case we mark the sink/source as offline but
there is no reconnect attempted later.
Added man page + more complex example which includes mixed usage of both input
and output.
Without this change yambar can't be installed/used without libmpdclient even for
people who do not use MPD. Let's make this optional.
We could put the optional module summary in the module meson.build but we'd have
to move summary() in main meson.build so that they appear in proper order.
