[Gtk-sharp-list] Generating returns instead of out params

[fd]

Right now, the code generator cunningly turns 

        static extern void gtk_text_buffer_get_start_iter(IntPtr raw,
        out Gtk.TextIter iter);

into

        public Gtk.TextIter StartIter {}

However,

        static extern void gtk_text_buffer_get_iter_at_offset(IntPtr
        raw, out Gtk.TextIter iter, int char_offset);

is still generated as

        public void GetIterAtOffset(out Gtk.TextIter iter, int
        char_offset) {}

Should we look into generating this instead?

        public Gtk.TextIter GetIterAtOffset(int char_offset) {}

Where in Parameters.cs would this particular manipulation be made? A lot
of the logic to detect this situation already seems to exist in there,
so I don't want to reinvent the wheel.