gvariant: Add g_variant_get() example for dicts
gvariant: Add g_variant_get() example for dicts

In the Dictionary section of the gvariant-format-strings documentation
only how to construct a dictionary is shown.

Add a small example showing how to extract data from a nested dictionary
and specifically from a GVariant of type "(oa{sa{sv})". Move also the
Dictionary section after the GVariant * section for the sake of clarity.

https://bugzilla.gnome.org/show_bug.cgi?id=786737

johne53/MB3Glib,johne53/MB3Glib,endlessm/glib,johne53/MB3Glib,endlessm/glib,endlessm/glib,johne53/MB3Glib,endlessm/glib,johne53/MB3Glib,johne53/MB3Glib,endlessm/glib