Python 3.8 does not support tuple[...], list[...], set[...] and so on.We will use the analogues from typing package: typing.Tuple[...], typing.List[...] and typing.Set[...].

This commit fixes a problem with imports.As I understand 3.8 has a problem with import across root-directory and I do not know/find how to fix it correctly.If someone know how to resolve these problems more easily (through sys.path/__init__.py?) - you are welcome!

We will run all the tests to get a full information about compatibility.Some new tests may fail.---TODO: may be it is better to compile/install required python version explicitly instead using pyenv.

This reverts commit96ddf19.It seems to me there was a local gluk. Let's test without these changes.