immerrr again

I have added a minimal test to exercise gunicorn worker logging, because it is true that previously there were no tests for this.

I have updated the branch according to the feedback, it's almost there: - the old default logging format is kept as is - the `--access-log-format` parameter still needs to be...

I have rebased to master and added `--access-log-format`, and looks like the test are passing: https://github.com/immerrr/uvicorn/actions/runs/957952813 I'm not sure I like the result: now it looks like there are two...

@Kludex @euri10 please, let me know if I can help somehow to push this forward

> Curious to hear your thoughts! To me it sounds like a nice and a straightforward solution. I would probably try to keep this PR focused on getting the gunicorn...

@Kludex @euri10 please, let me know if I can help somehow to push this forward

> Just for the record, we also need to update the documentation. I have rebased the PR to latest master and taken a stab at the documentation. Please, let me...

> I have rebased the PR to latest master and taken a stab at the documentation. Just updated the PR again to resolve merge conflicts. @Kludex @euri10 would be great...

It could be nicer to extend the existing `retry_if_exception` to accept `match` kwarg, like [pytest.raises does](https://docs.pytest.org/en/latest/assert.html#assertions-about-expected-exceptions): ``` retry_if_exception(MyException, match='zzz') retry_if_exception(MyException, match=some_precompiled_regexp) ```

@DanEEStar the way I handle time at least in synchronous tests is that I use a datetime-mock library, my preferred one is [freezegun](https://github.com/spulec/freezegun) but feel free to use any other....