* also remove the PyGIArgCleanup sinature as GDestroyNotify works just fine

* We now can invoke with in values
* out, constructors and returns still don't work along with numerous complex
  in types

* caching stage is hooked up but not used yet
* throws exceptions for everything that can not be cached yet

* simplify what we pass into the arg cache generators so we may use them
  for geneating marshalling caches for container items, not just arguments

* still doesn't compile

* this does not compile and is not hooked up to the build system
* lays out the caching data structures and some skeleton functions

https://bugzilla.gnome.org/show_bug.cgi?id=637832

https://bugzilla.gnome.org/show_bug.cgi?id=637615

* There are still some cavets in Python 2:
  - properties are returned as String objects with the unicode code points
  - you must add # coding=utf-8 to the top of your python file or python
    will error out if it sees embeded unicode charaters (such as when
    supporting python 3 and python 2 from the same source)

https://bugzilla.gnome.org/show_bug.cgi?id=620579

	* codegen/docextract_to_xml.py: Print the xml of the gtk-doc block in
	alphabetical order according to the identifier (function name) so that
	the generation of xml files in the C++ bindings is deterministic.
	Thanks to Krzesimir Nowak for suggesting this in a gtksourceviewmm
	recent commit.

I must take a Pango.Context argument. Unfortumately the context is not a
gobject property so we need to jump through some oops.

It is now properly handled by an override.

https://bugzilla.gnome.org/show_bug.cgi?id=636486