Major rewrite

One of the first big changes in this rewrite is changing the Type
object to have separate target_fundamental and target_giname properties,
rather than just being strings.  Previously in the scanner, it was
awful because we used heuristics around strings.

The ast.py is refactored so that not everything is a Node - that
was a rather useless abstraction.  Now, only things which can have
a GIName are Node.  E.g. Type and Field are no longer Node.

More things were merged from glibast.py into ast.py, since it isn't
a very useful split.

transformer.py gains more intelligence and will e.g. turn GLib.List
into a List() object earlier.  The namespace processing is a lot
cleaner now; since we parse the included .girs, we know the C
prefix for each namespace, and have functions to parse both
C type names (GtkFooBar) and symbols gtk_foo_bar into their
symbols cleanly.  Type resolution is much, much saner because
we know Type(target_giname=Gtk.Foo) maps to the namespace Gtk.

glibtransformer.py now jus...