Examples

[jeroenrinzema]

As discussed in #1099. This PR adds a simple consumer group example as a sort of cheat sheet for developers already working with Sarama or new developers interested in using Sarama.

More examples could be created for for example the Kafka Sarama admin client. Please tell me if someone is interested in more examples, I could include them into this PR.

[bai]

Thanks for this!

There seem to be a valid errcheck failure on CI:

errcheck -ignorepkg fmt github.com/Shopify/sarama/...
examples/consumergroup/main.go:83:19:	go client.Consume(ctx, strings.Split(topics, ","), &consumer)
examples/consumergroup/main.go:93:14:	client.Close()
make: *** [errcheck] Error 1
travis_time:end:089e1ade:start=1552059645250063283,finish=1552059649462728896,duration=4212665613
�[0K�[31;1mThe command "make errcheck" exited with 2.�[0m