doc: make all manpages with Doxygen

Use (fixed-up) Doxygen manpage output for all program & module manpages.

This also allows formatting the manual pages properly in the HTML docs.

The Markdown pages work properly only with Doxygen >= 1.9.7, older
versions put them to wrong place in the HTML docs.

doc/dox/programs/libpipewire-modules.7.md

@@ -0,0 +1,44 @@
+\page page_man_libpipewire-modules_7 libpipewire-modules
+
+PipeWire modules
+
+# DESCRIPTION
+
+A PipeWire module is effectively a PipeWire client running inside
+`pipewire(1)` which can host multiple modules. Usually modules are
+loaded when they are listed in the configuration files. For example the
+default configuration file loads several modules:
+
+    context.modules = [
+        ...
+        # The native communication protocol.
+        {   name = libpipewire-module-protocol-native }
+
+        # The profile module. Allows application to access profiler
+        # and performance data. It provides an interface that is used
+        # by pw-top and pw-profiler.
+        {   name = libpipewire-module-profiler }
+
+        # Allows applications to create metadata objects. It creates
+        # a factory for Metadata objects.
+        {   name = libpipewire-module-metadata }
+
+        # Creates a factory for making devices that run in the
+        # context of the PipeWire server.
+        {   name = libpipewire-module-spa-device-factory }
+        ...
+    ]
+
+# KNOWN MODULES
+
+$(LIBPIPEWIRE_MODULES)
+
+# AUTHORS
+
+The PipeWire Developers <$(PACKAGE_BUGREPORT)>;
+PipeWire is available from <$(PACKAGE_URL)>
+
+# SEE ALSO
+
+\ref page_man_pipewire_1 "pipewire(1)",
+\ref page_man_pipewire_conf_5 "pipewire.conf(5)"