Make Pywikibot also work under new versions of Python (3.8).
We are aiming for a multi-compatible codebase (3.5-3.7 and in the near future 3.9, 4.0 in few years), without a dependency on six. This means we do have some hacks (try-except import blocks, 'PYTHON_VERSION >= (3, 6): <do something different>', etc.