Add additional factory methods to Kinesis to create Akka Source

[htimur]

As the result of the issue with graceful shutdown of the KinesisConsumer described in #60, I added the additional methods to create the Akka Source with explicitly pathing the ConsumerService, for the better controll of the shutdown process.

[markglh]

Thanks for this!

It's weird that this isn't firing for you:
https://github.com/WW-Digital/reactive-kinesis/blob/master/src/main/scala/com/weightwatchers/reactive/kinesis/consumer/KinesisConsumer.scala#L251

Seems like the consumer is shutting down before that. Happy to merge this but would you mind adding this to the readme too please with an example?
https://github.com/WW-Digital/reactive-kinesis#akka-stream-source

[htimur]

@markglh Ok will update the docs and then the PR.

[coveralls]

Coverage decreased (-0.6%) to 89.522% when pulling 462539a on htimur:master into c635b6f on WW-Digital:master.

[htimur]

@markglh Please review the changes

[markglh]

LGTM, thanks!!