move GLib and GObject inside Vips

[jcupitt]

It would be neater to have the GLib and GObject modules inside Vips, see #119 (comment)

Though I wonder if this would be useful in practice. You can't have two glib or gobject libraries loaded into your program at once, since they both have plenty of global state, so two GLib modules would probably be a disaster.

[mvz]

I suppose this depends on whether you want ruby-vips to be loaded together with ruby-gnome2. IMHO, this should definitely be supported.

[jcupitt]

You're right, it should be possible. I'll have another go.

[jcupitt]

Aside: @mvz, I copied the ruby-vips inheritance stuff from your example (you probably noticed), so thank you very much!

https://github.com/jcupitt/ruby-vips/blob/master/example/inheritance_with_refcount.rb