* Add Flake8 configuration

Uses the configuration from ci_scripts

* Add mypy configuration file

Based on the ci_scripts parameters.

* Pre-commit mypy flake8, add flake8 excludes

Any venv folder does not need flake8.
The example directory got flake8 warnings so I assumed it should be
excluded.

* Add Black to pre-commit

Add ignore E203 as Black will observe PEPs specification for white space
around a colon it is next to an expression.

* Set max line length to 100

* Blacken code

There are a few places where big indentation is introduced that may
warrant refactoring so it looks better.
I did not refactor anything yet, but did exlude three (?) lists (of ids)
to not be formatted.

* Add unit tests to flake8 and mypy pre-commit

* Use pre-commit for flake8, mypy and black checks

This ensures it runs with the same versions and settings as developers.

* Update docs, add 'test' dependencies

Add two other developer dependencies not strictly required for unit
tests, but required for development.
I think the overlap between people who want to execute unit tests and
perform commits is (close to) 100% anyway.

* Uninstall pytest-cov on appveyor ci

It seems to cause an error on import due to a missing sqlite3 dll.
As we don't check coverage anyway, hopefully just uninstalling is
sufficient.

* Add -y to uninstall

* Sphinx issue fix (#923)

* Sphinx issue fix

* Removing comment

* More robust handling of openml_url (#921)

I ran into issues when the openml server config is not exactly 'https://www.openml.org/api/v1/xml', e.g. I had 'https://www.openml.org/api/v1'.
I only noticed when getting a bad dataset url.

This edit makes the API more robust against how exactly the server URL is set in the config.

* format for black artifacts

* Add Flake8 configuration

Uses the configuration from ci_scripts

* Add mypy configuration file

Based on the ci_scripts parameters.

* Pre-commit mypy flake8, add flake8 excludes

Any venv folder does not need flake8.
The example directory got flake8 warnings so I assumed it should be
excluded.

* Add Black to pre-commit

Add ignore E203 as Black will observe PEPs specification for white space
around a colon it is next to an expression.

* Set max line length to 100

* Blacken code

There are a few places where big indentation is introduced that may
warrant refactoring so it looks better.
I did not refactor anything yet, but did exlude three (?) lists (of ids)
to not be formatted.

* Add unit tests to flake8 and mypy pre-commit

* Use pre-commit for flake8, mypy and black checks

This ensures it runs with the same versions and settings as developers.

* Update docs, add 'test' dependencies

Add two other developer dependencies not strictly required for unit
tests, but required for development.
I think the overlap between people who want to execute unit tests and
perform commits is (close to) 100% anyway.

* Uninstall pytest-cov on appveyor ci

It seems to cause an error on import due to a missing sqlite3 dll.
As we don't check coverage anyway, hopefully just uninstalling is
sufficient.

* Add -y to uninstall

* format for black artifacts

Co-authored-by: Neeratyoy Mallik <neeratyoy@gmail.com>
Co-authored-by: Joaquin Vanschoren <joaquin.vanschoren@gmail.com>