gst_discoverer_discover_uri() expects the caller to unref the returned
GstDiscovererInfo object. The corresponding gtk-doc annotation was not
updated to reflect this.
There's no reason to make the marshaller public API. Don't install
pbutils-marshal.h header file and use prefix that makes sure the
symbol doesn't get exported.
While the doc parser allows for certain variation, it is a good idea to not
use random characters here and there, but try to stick to the little markup
syntax there is.
