Allow integer md_header_level

[makukha]

A simple change fixing #90.

I tried to be as conservative as possible, letting md_header_level remain str internally and be converted from int on input. This change is backwards compatible and allows string values as before.

[nedbat]

Thanks! Can you take a look at the linter failures?

[nedbat]

Also, do you want to make a scriv fragment for the changelog? :)

[nedbat]

BTW, I just fixed the test suite issues, if you rebase on top of master.

[makukha]

@nedbat, thank you for the advice! I fixed the lint errors and managed to add some test, as well as the changelog fragment. Please feel free to change this PR, if needed, to match the the project standards. And thank you for the scriv :)

[makukha]

It seems that tests failures are not related to my changes

[nedbat]

They are related: you can't test TOML support on a version without toml lib. You need this line from the tests a few above yours:

@pytest.mark.skipif(tomllib is None, reason="No TOML support installed")

[makukha]

Yes, my bad, I misinterpreted the tox log. Fixed.

[nedbat]

Thanks!