Update to use AWS SDK for PHP version 2.

Problem/Motivation

I need to get AWS SQS working and was unable to do it with the current 7.x-1.x branch.

Proposed resolution

As I was poking around and trying to debug I realized tons of AWS examples, videos, etc. all reference version 1 of the SDK, but the doc all point to version 2. I'm not 100% sure where CEikermann/AmazonSQS (included in the composer recipe) comes from. But I went ahead and swapped this out for AWS's official SDK and refactored AwsSqsQueue to use this for the plumbing and now everything seems to be working great.

(I was a little reluctant to abandon CEikermann/AmazonSQS without really knowing why this was chosen in the first place. But for my project and probably other enterprise Drupal sites, I suspect it's actually preferable to use AWS's official SDK simply because it's the official SDK.)

While I was refactoring things, I also found and fixed two bugs:

• Before, if you enabled awsSqsQueue as your queue backend, unchecking this setting on the config page did not actually disable the SQS backend.
• There are were some code comments that said SQS didn't support "releasing" a claim on an item in the queue. Turns out, SQS does support this. Their terminology is just different. They call this a "Visibility Timeout". So I went ahead and implemented this method.

Remaining tasks

• Determine if maintainers are supportive of moving the project in this direction
• Decide if this patch should be applied to the 1.x branch or a new 2.x branch (if people depend on third party libraries included in the 1.x branch, that's probably a good reason to put this in 2.x)
• If this is going to get turned into a 2.x, it's probably worth back porting the fixes mentioned above to the 1.x branch (I'm happy to help pull those patches out)

User interface changes

• Added more documentation on admin config page
• Now the setting to turn SQS into the queue backend is a drop-down, not a checkbox
• AWS regions are configurable on the admin config form
• Added README file with setup instructions for newbies to AWS services and composer / composer_manager

API changes

• Removed CEikermann/AmazonSQS in composer.json
• Removed https://github.com/nickveenhof/AmazonSQS repo in composer.json
• Added aws/aws-sdk-php in composer.json
• Renamed class: awsSqsQueue -> AwsSqsQueue

Related Issues

Development and more granular patches (commit-by-commit) are posted in a pull request on GitHub:
https://github.com/bryanhirsch/aws_sqs/pull/1

Original report by bryanhirsch