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.

examples/configurations/laptop.conf

@@ -226,6 +226,54 @@ bar:
                     "":
                       - string: {text: , font: *awesome, foreground: ffffff66}
                       - string: {text: "{ssid}", foreground: ffffff66}
+    - pulse:
+        anchors:
+          - string: &common {on-click: "pavucontrol"}
+          - string: &offline {foreground: dc322fff}
+          - string: &muted {foreground: 839496ff}
+          - in: &in
+            - string: {<<: *common, text: "", font: *awesome}
+            - string: {<<: *common, text: "{source_percent}%"}
+          - out: &out
+            - string: {<<: *common, text: "🔊︁", font: *awesome}
+            - string: {<<: *common, text: "{sink_percent}%"}
+          - in_muted: &in_muted
+            - string: {<<: [*common, *muted], text: "", font: *awesome}
+            - string: {<<: [*common, *muted], text: "{source_percent}%"}
+          - out_muted: &out_muted
+            - string: {<<: [*common, *muted], text: "", font: *awesome}
+            - string: {<<: [*common, *muted], text: "{sink_percent}%"}
+
+        content:
+          map:
+            tag: sink_online
+            values:
+              false:
+               - string: {<<: [*offline, *common], text: , font: *awesome}
+              true:
+                map:
+                  tag: sink_muted
+                  values:
+                    true:
+                      map:
+                        tag: source_muted
+                        values:
+                          true:
+                            - *out_muted
+                            - *in_muted
+                          false:
+                            - *out_muted
+                            - *in
+                    false:
+                      map:
+                        tag: source_muted
+                        values:
+                          true:
+                            - *out
+                            - *in_muted
+                          false:
+                            - *out
+                            - *in
     - alsa:
         card: hw:PCH
         mixer: Master