Add scalar value formatter
Add AWS DynamoDB handler

This also adds the `aws/aws-sdk-php` dev dependency
Refactor scalar formatter

Removed some of its own logic in favor of extending NormalizerFormatter to
benefit from shared logic.
Merge remote-tracking branch 'adlawson/dynamodb-handler'

Conflicts:
	README.mdown
	composer.json
Add version check for the AWS SDK, refs #260