Make it possible to replace inline code with python version

[lazka]

api/Gtk_3.0/classes/TreeModelSort

Possible solution:

Each python code fragment is saved in "Namespace-Version-Attribute-.py" e.g. "Gtk-3.0.TreeModelSort-fcc1cdba86b0c37d532480f7e7e3ecf2.py".

The hash gets computed using the C inline code. pgi-docgen replaces it with the python code or notifies if a code file isn't used anymore and needs updating/review.

[lazka]

On a second though, not worth it. Time is better spend on actual documentation with proper examples.

[lazka]

And reopen, here is how valadoc does it: https://github.com/flobrosch/valadoc-org/tree/master/examples