Use less specific types in validators args

[kalekseev]

Make it possible to use Tuple[str]

[kalekseev]

@mkurnikov replaced Iterable with Collection.

Also what do you think about adding pyproject.toml file with black configuration (line length = 120) otherwise editors reformats with default line length?
I can also setup pre-commit with black, isort and flake8.

[mkurnikov]

Sure, I would gladly accept a PR with those changes. Let's start with the pyproject.toml, and add pre-commit hooks later.