Add `--ignore-warnings` argument

[amureki]

In my usecase, I want to show warnings to the developer (via pre-commit), but don't want to output them in CI. Here such setting would be handy.

P.S. I am basing this PR on top of #45 as it has fixed tests suite, which is needed here.

[codecov[bot]]

Codecov Report

Patch coverage: 100.00% and no project coverage change

Comparison is base (8a4491e) 100.00% compared to head (653d16c) 100.00%.

Additional details and impacted files

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[amureki]

@codingjoe I addressed text comment. Regarding rich and click - wonderful idea, I like these packages and agree that they are well-maintained and can improve DX here.

But this (especially click) could be a bigger change, so we'd better go with it separately. What do you think?