New SASL/SCRAM support

[fbricon]

Added SASL/SCRAM-256 and SASL/SCRAM-512 authentication mechanisms:

Tested against a https://www.cloudkarafka.com/ cluster (Free Tier) :

• connection works (using SCRAM-256)
• listing brokers, topics, consumer group works
• producing messages works

There are some things that still don't work against the karafka clusters:

• creating a topic fails (looks like authorization limitation), even when using the user prefix for the topic name
• adding/starting a consumer fails (complains about SASL mechanism not supported) fixed

Fixes #3

[fbricon]

The consumer issue was fixed.
AFAICT, everything works as expected.

[dentarg]

creating a topic fails (looks like authorization limitation), even when using the user prefix for the topic name

Have you tried prefixing consumer group name with the username? CloudKarafka/python-kafka-example@365850e

[fbricon]

@dentarg on cloudkarafka, topic creation fails, even with the username prefix. But I could reproduce the same behaviour with a simple java client.
Consumer creation works, even without the username prefix

[fbricon]

CloudKarafka said everything works on their instances: https://twitter.com/CloudKarafka/status/1350071031336153089
I think we're good to go.

[angelozerr]

Works like a charm with my cloudkafka cluster, great job @fbricon !