Goka Versions Save

• add mutex to codex-map in tester to prevent concurrent map access

• Add EmitSyncWithHeaders to Emitter (by @adw1n)
• Prefix sarama logger with [Sarama] (by @adw1n)
• Bugfix in example (by @FredrikBakken)

Fixing the processor and view state in the monitoring web-ui.

Add Commit() to MockConsumerGroupSession and cgSession to be compatible with ConsumerGroupSession interface.

With this release we integrate sarama consumer group into goka and remove the sarama-cluster dependency. These changes enable users to use goka with recent sarama versions.

removed race condition in stats tracking fixed panic in View.Get for uninitialzed state call Open on storage after init

Major changes:

• Removed sarama-cluster, replaced with sarama's ConsumerGroup
• remove package kafka, move remaining files to root
• introduce go mod
• removed support for librdkafka

See #239 for details