Update the URLs of API_DOCUMENTATION
Update the hrefs for the following libraries and tutorials at API_DOCUMENTATION
GTK+/Glib Libraries
- GLib
fromhttps://developer.gnome.org/glib/stable/
tohttps://docs.gtk.org/glib/
- GIO
fromhttps://developer.gnome.org/gio/stable/
tohttps://docs.gtk.org/gio/
- GDK
fromhttps://developer.gnome.org/gdk3/stable/
tohttps://docs.gtk.org/gdk3/
- GTK
fromhttps://developer.gnome.org/gtk3/stable/
tohttps://docs.gtk.org/gtk3/
Xfce Developer Tutorials
GTK+ 3 Tutorial (Official)
from https://developer.gnome.org/gtk3/stable/gtk-getting-started.html
to https://docs.gtk.org/gtk3/