Automatically add stem to GObject method names

Automatically add stem to GObject method names

For example, this:

	extern(GObject):
		interface GtkWidget:
			void show()

	GObject obj
	obj.show()

becomes

	gtk_widget_show(obj)

Name is lower-cased, and an _ inserted before each upper case letter that
follows a lower case one. Might need to way to state the stem explicitly
for some types.