Support PurgeQueue (in newer AWS Java SDK)

[theJenix]

Amazon has added a PurgeQueue method to its SQS API, and I think it would be useful for this library to support it (see https://aws.amazon.com/about-aws/whats-new/2014/12/08/delete-all-messages-in-an-amazon-sqs-queue/). To do so, it would require bumping the AWS Java SDK version to at least 1.9.10. I can submit a PR for this with appropriate changes to support the newer SDK, but before I do I wanted to see if this is something you would likely accept.