chore: improve GitHub integration, add CI config

[bednar]

This PR introduce support for CI integration (next PRs will enable code style checks) add templates for GitHub issues, ...

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[karel-rehor]

@bednar Can you double check line 50 of setup.py? While python 3.7 was removed from classifiers, it is still included there as part of the logic of python_requires.

Otherwise, looks great.

[karel-rehor]

Looks good.