Fix gtkD api display

[Johnson Jones via Digitalmars-d-learn]

Also, interfaces are not linkable.

e.g., for gtk.ApplicationWindow, it inherits from gtk.Window but 
I have to go back to the packages and scroll down to find 
gtk.Window to see it's properties and methods. Would be nice if I 
could just click on the gtk.Window and it jump me to it.

https://api.gtkd.org/gtkd/gtk/ApplicationWindow.html

class ApplicationWindow : gtk.Window.Window, 
gio.ActionGroupIF.ActionGroupIF, gio.ActionMapIF.ActionMapIF;

since the hierarchy is gtk/Window/Window, click on gtk should 
take one to the gtk package, the first Window should take one to 
gtk.Window and the second should take one to gtk.Window.Window