Merging aio-libs/aiokafka into robinhood/aiokafka 1.1

[forsberg]

This is a merge of aio-libs/aiokafka into robinhood/aiokafka 1.1, made to the best of my abiliites - and that's meant as a warning, as it was a pretty complex merge with lot's of conflicts, and I'm not very familiar with this library.

Nevertheless, I made this attempt as I really needed the SASL-SCRAM-256/512 authentication support. I have got it working with faust with a few changes (See my 1.10-scram-sha-sasl-mechanism branch.

Is robinhood/aiokafka really needed anymore? It's unclear to me why it was forked, perhaps what was missing has now been added to aio-libs/aiokafka so the extra work can be avoided?