After write hook

This is related to pr https://github.com/fluent/fluent-plugin-s3/pull/43

We implemented a really simple after write hook. Our idea is that the after write scripts would have to have and maintain their own configs, including all the AWS key/secret key configurations. 

I've included a sample after write hook that sends a message to SQS on write, and a config file that would go with it. These are included simply as examples.