Enable possibility for RawConsumers to use SuperStreams

[jonnepmyra]

Had a quick chat with @Gsantomaggio about this..

This opens up the possibility to use a RawConsumer (with all it options) with SuperStream capabilities which has advantages in some edge-case-scenarios like:

• You need to start a consumer for a single partition, and not all partitions of the superstream
• You need specific event-callbacks for each partition in the SuperStream
• You want to implement your own ConnectionClosedHandler and/or MetadataHandler

[Gsantomaggio]

Thank you for the PR. We are busy atm with the 1.2 release. I will check as soon as possible!

[Gsantomaggio]

Closed in favour of #250