Updated language for consistency with SQS.

	modified:   aws_sqs.admin.inc
Changed composer. Use AWS SDK for PHP, version 2.

 	modified:   composer.json
Changed awsSqsQueue class to use AWS SDK for PHP v2.

	modified:   aws_sqs.queue.inc
Updated admin config form.

  Added documentation and clarification. Surfaced some variables that weren't
  exposed earlier.

	modified:   aws_sqs.admin.inc
Fixed bug in admin form preventing disabling awsSqsQueue as default.

  Before, once you checked the box to set awsSqsQueue as your default, there was
  no way to disable this. You could uncheck the box. But it wouldn't switch you
  back to Drupal's default queue backend.

	modified:   aws_sqs.admin.inc