Document best practices for high level consumer functionality

[alpe]

I ran into #36 and was wondering how others build high High level consumer functionality?
Would be great to document/ share some ideas/ code about

• building consumer groups
• persisting last message read offsets
• deduplicate messages
  ...

[zorkian]

And for cross-linking, here is one attempt at Kafka consumer coordination: https://github.com/zorkian/marshal

(Only commenting with this link b/c I know optiopay has expressed they won't be working on this for now, and I am generally a fan of not having huge libraries that do everything.)