docs: Use generic marshallers in GObject how-to examples
docs: Use generic marshallers in GObject how-to examples

They’re the new vogue for handling signals.

https://bugzilla.gnome.org/show_bug.cgi?id=744060

endlessm/glib,johne53/MB3Glib,cention-sany/glib,tchakabam/glib,ieei/glib,Distrotech/glib,ieei/glib,endlessm/glib,MathieuDuponchelle/glib,ieei/glib,tchakabam/glib,mzabaluev/glib,endlessm/glib,endlessm/glib,MathieuDuponchelle/glib,ieei/glib,cention-sany/glib,Distrotech/glib,cention-sany/glib,gale320/glib,mzabaluev/glib,johne53/MB3Glib,Distrotech/glib,gale320/glib,Distrotech/glib,cention-sany/glib,mzabaluev/glib,gale320/glib,MathieuDuponchelle/glib,johne53/MB3Glib,ieei/glib,mzabaluev/glib,endlessm/glib,gale320/glib,cention-sany/glib,johne53/MB3Glib,johne53/MB3Glib,tchakabam/glib,tchakabam/glib,Distrotech/glib,MathieuDuponchelle/glib,tchakabam/glib,gale320/glib,johne53/MB3Glib,MathieuDuponchelle/glib,mzabaluev/glib