Before the change, the engine didn't call the `Close()` method of the
sinks. This is needed in some cases, i.e when a sink implementation is
buffered.
This change adds a `Close()` method to the registry that
will signal sinks to exit and wait for all sinks to exit before
returning. This is then used in the engine stop logic.
In the channel-based registry, the closing of all sinks is done in
parallel (using a `sync.WaitGroup`). In the sync registry, sinks are
closed sequentially.
Fixes issue #10
This new sink adds basic support for Kafka, using `sarama.SyncProducer`.
It allows minimal configuration to make it useful:
- Topic
- Broker List
- TLS settings
The layout transformations are supported in the same way as for kinesis.
Implements issue #6.
Mustafa Akın
Marc Demierre