Add KafkaMetricsRegistry

[Z1kkurat]

This issue addresses #237.

Please read the updated README.md, it contains the reasoning behind the change and a full (I hope) description of the new API.

Let me know what you think about it.

[t3hnar]

hm, are we sure it should be module of smetrics and not skafka ?

[Z1kkurat]

hm, are we sure it should be module of smetrics and not skafka ?

@t3hnar This is a good question. On the one hand, I agree that this code doesn't depend on anything from smetrics and could be placed in skafka. On the other hand, the whole essence of it is collecting metrics, I don't think it makes much sense without having KafkaMetricsCollector to expose the collected metrics and it was created to overcome the limitations of KafkaMetricsCollector (being a Prometheus collector).

But I like the idea of moving it to skafka. I'll start working on it.

[Z1kkurat]

@t3hnar thanks for the idea, PR to skafka with the identical content: evolution-gaming/skafka#324

[stasimus]

@Z1kkurat should we keep this PR?