add azure pipeline for tests, and enforce black, flake8 and isort for commits

[rytilahti]

Up for discussion :-) Having all formating enforced by the pre-commit makes it easy to contribute without having to worry about that. Travis, Hound, and Coveralls could be disabled in the future.

I'd prefer adding mypy checks also, but that will require a bit more work to make it happen.

• Add pre-commit hooks for flake8, isort.
• Use azure dev for running precommit checks and tests.
• Use black's default line length (88) instead of (100). This seems to work fine.

[syssi]

Awesome! Let's give it a try. Feel free to merge.