This will apply to 2.1+. As of Twig 1.12, creating a Twig extension is slightly different. For example, Twig_Function_Function is replaced by Twig_SimpleFunction.
Both the old and new version of the Twig docs are maintained, which is nice for comparison:
http://symfony.com/doc/master/cookbook/templating/twig_extension.html should be updated with the new way to go, right?
Yes, Ryan is talking about that document.
Ok, I can take this one if you are ok with it.
of course! Do what you can! :)