Python 3.9 have been released as stable on [October 5th 2020](https://www.python.org/dev/peps/pep-0596/) ## Tasks - [x] Create v3.9 container: docker/python3/poetry!1 - [x] Fix C(++) dependencies which do not provides wheels - [x] [`aiohttp` v3.7.x](https://github.com/aio-libs/aiohttp/blob/master/CHANGES.rst#371-2020-10-25) allows to use `multidict` 5.0.0 which has pre-built wheels for Py3.9, [not the previous version](https://pypi.org/project/multidict/4.7.6/). But, [`multidict` v5.0 also drops Py 3.5 support](https://github.com/aio-libs/multidict/blob/master/CHANGES.rst#500-2020-10-12). This has to be dropped from Silkaj too. - [x] `cffi` used from `pynacl` - [x] #176: Get rid of `pynacl`: `pynacl` is using an old version of `cffi` which is not built for py3.9. getting rid of pynacl from silkaj could allow us to remove `libffi-dev`. duniterpy#83 is planning to use pynacl. - [x] `typed-ast`, a dependency of `black` is not pre-built for Py3.9. [Now provided](https://github.com/python/typed_ast/issues/146). - [x] Set-up `tests-3.9` job