Prometheus-kafka-consumer-group-exporter

Bug Fixes:
- [[12](https://github.com/braedon/prometheus-kafka-consumer-group-exporter/issues/12)] Require kafka-python 1.3.x, 1.4+ drops the .schedule() method on clients

Enhancements:
- [[9](https://github.com/braedon/prometheus-kafka-consumer-group-exporter/issues/9)] Add low-water mark metric (thanks rdonnelly3)
- [[8](https://github.com/braedon/prometheus-kafka-consumer-group-exporter/issues/8)] Add lag and lead metrics

Breaking Changes:
- Default port changed from 8080 to 9208, [see here for why](https://github.com/prometheus/prometheus/wiki/Default-port-allocations)

Enhancements:
- Add high-water mark metric ([allows calculating lag](https://github.com/braedon/prometheus-kafka-consumer-group-exporterlag))
- Support configuring the consumer via properties files
- Allow setting arbitrary logging levels