Add initial pulseaudio module support

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.

doc/meson.build

@@ -9,6 +9,7 @@ foreach man_src : ['yambar.1.scd', 'yambar.5.scd', 'yambar-decorations.5.scd',
                    'yambar-modules-foreign-toplevel.5.scd',
                    'yambar-modules-i3.5.scd', 'yambar-modules-label.5.scd',
                    'yambar-modules-mpd.5.scd', 'yambar-modules-network.5.scd',
+                   'yambar-modules-pulse.5.scd',
                    'yambar-modules-removables.5.scd', 'yambar-modules-river.5.scd',
                    'yambar-modules-script.5.scd', 'yambar-modules-sway-xkb.5.scd',
                    'yambar-modules-sway.5.scd', 'yambar-modules-xkb.5.scd',

doc/yambar-modules-pulse.5.scd

@@ -0,0 +1,62 @@
+yambar-modules-pulse(5)
+
+# NAME
+pulse - Monitors one pulseaudio source and sink for volume and mute/unmute changes
+
+# TAGS
+
+[[ *Name*
+:[ *Type*
+:[ *Description*
+|  online
+:  bool
+:  True when the Pulseaudio connection has successfully been opened
+|  sink_online
+:  bool
+:  True when the Pulseaudio sink (output) exists and is usable
+|  source_online
+:  bool
+:  True when the Pulseaudio source (input) exists and is usable
+|  sink_percent
+:  range
+:  Sink (output) volume level in percentage, with min and max as start and end range values
+|  source_percent
+:  range
+:  Source (input) volume level in percentage, with min and max as start and end range values
+|  sink_muted
+:  bool
+:  True if sink is muted, otherwise false
+|  source_muted
+:  bool
+:  True if source is muted, otherwise false
+
+
+# CONFIGURATION
+
+[[ *Name*
+:[ *Type*
+:[ *Req*
+:[ *Description*
+|  sink_name
+:  string
+:  no
+:  Sink name to monitor. Defaults to _@DEFAULT\_SINK@_
+|  source_name
+:  string
+:  no
+:  Source name to monitor. Defaults to _@DEFAULT\_SOURCE@_
+
+
+# EXAMPLES
+
+```
+bar:
+  left:
+    - pulse:
+        content: {string: {text: "{sink_percent} %"}}
+```
+
+# SEE ALSO
+
+*yambar-modules*(5), *yambar-particles*(5), *yambar-tags*(5), *yambar-decorations*(5)
+