Prometheus-kafka-consumer-group-exporter

Bug Fixes:
- [[30](https://github.com/braedon/prometheus-kafka-consumer-group-exporter/issues/30)] Exclude kafka-python versions 1.4.5 and 1.4.6 due to performance issues.

Enhancements:
- [[35](https://github.com/braedon/prometheus-kafka-consumer-group-exporter/pull/35)] Change `__consumer_offsets` key parsing error logs to warnings (thanks jutley)

Bug Fixes:
- [[33](https://github.com/braedon/prometheus-kafka-consumer-group-exporter/pull/33)] Fix exporter offset to track the offset of the next message, not the current one, to make offset/lead/lag metric semantics consistent (thanks jutley)

Bug Fixes:
- [[29](https://github.com/braedon/prometheus-kafka-consumer-group-exporter/issues/29)] Remove metrics for deleted consumer groups (thanks jutley)

Bug Fixes:
- [[28](https://github.com/braedon/prometheus-kafka-consumer-group-exporter/issues/28)] `__consumer_offsets` messages from Kafka 2.1+ not supported

Breaking Changes:
- `kafka_consumer_group_commits` metric renamed to `kafka_consumer_group_commits_total`, [due to change in Prometheus client](https://github.com/prometheus/client_python/releases/tag/v0.4.0)

Enhancements:
- [[27](https://github.com/braedon/prometheus-kafka-consumer-group-exporter/pull/27)] Add `kafka_consumer_group_commit_timestamp` metric to track time of the last commit from a consumer group (thanks jutley)

Bug Fixes:
- [[15](https://github.com/braedon/prometheus-kafka-consumer-group-exporter/pull/15)] `--bootstrap-brokers` default value shouldn't override value in consumer config file (thanks jsargiot)
- [[18](https://github.com/braedon/prometheus-kafka-consumer-group-exporter/issues/18)] Fix memory leak with Python 3.7
- [[21](https://github.com/braedon/prometheus-kafka-consumer-group-exporter/issues/21)] Don't let lag metrics go below 0
- [[22](https://github.com/braedon/prometheus-kafka-consumer-group-exporter/issues/22)] Handle exception parsing strange `__consumer_offset` messages (thanks jutley)

Enhancements:
- [[12](https://github.com/braedon/prometheus-kafka-consumer-group-exporter/issues/12)] Rework to not require .schedule() method on clients from kafka-python 1.3.x, adding support for 1.4+