Fix gtkD api display

[Adam D. Ruppe via Digitalmars-d-learn]

On Friday, 4 August 2017 at 02:08:31 UTC, Johnson Jones wrote:
> https://api.gtkd.org/gtkd/gtk/ApplicationWindow.html

So I ran gtkd through my doc generator too

http://dpldocs.info/experimental-docs/gtk.ApplicationWindow.ApplicationWindow.html

and I didn't make a top-level package file either... but doing 
that wouldn't be hard. However, I noticed it is basically the 
same as the official C documents: 
https://developer.gnome.org/gtk3/stable/GtkApplicationWindow.html 
so idk if it is worth spending a lot of time on it.