gerror: Document advantages of GError over numeric error codes
gerror: Document advantages of GError over numeric error codes

Despite knowing about GError, there are multiple cases where developers
have still used traditional numeric error codes, and then got themselves
into a mess about bindability and generation of error messages.

Try and avoid this by including a brief paragraph on the benefits of
GError over EINVAL-style error codes.

https://bugzilla.gnome.org/show_bug.cgi?id=743011

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