Port gtk-doc comments to their equivalent markdown syntax

Modernizing our documentation and preparing a possible move to hotdoc.
This commits also adds missing @title metadatas to all SECTIONs
diff --git a/gst/gstdevicemonitor.c b/gst/gstdevicemonitor.c
index d03a813..79c65ce 100644
--- a/gst/gstdevicemonitor.c
+++ b/gst/gstdevicemonitor.c
@@ -21,6 +21,7 @@
 
 /**
  * SECTION:gstdevicemonitor
+ * @title: GstDeviceMonitor
  * @short_description: A device monitor and prober
  * @see_also: #GstDevice, #GstDeviceProvider
  *
@@ -34,7 +35,6 @@
  * The device monitor will monitor all devices matching the filters that
  * the application has set.
  *
- *
  * The basic use pattern of a device monitor is as follows:
  * |[
  *   static gboolean