API stability

Hi there, I'm the maintainer of pytest-codecov.

Since this is technically a CLI tool I was wondering whether you provide any sort of stability guarantees for some of the API used internally to implement the several commands.

I would like to integrate codecov-cli into pytest-codecov in the near future, so we can provide new features with an overall lower maintenance burden. But I would prefer to use the internal API directly rather than invoke the CLI through a subprocess or click.CliRunner, since that would force me to write some of the reports to disk first and would also incur the risk of sending reports from previous runs, because they were not properly cleaned up.

I would also be open to the possibility of transferring ownership of the pytest plugin over to you, if you feel like there is some benefit to providing an official pytest plugin.