[docs] [issue18355] Merge super() guide into documentation

Raymond Hettinger added the comment: I'll translate it into a How-to guide when I get a chance. Right now, the content is in great shape, but the tone is somewhat "blog-posty". For now, the external link will have to suffice. ---------- priority: normal -> low _______________________________________ Python tracker <report@bugs.python.org> <http://bugs.python.org/issue18355> _______________________________________