Update of SQS to API version 2012-11-05

These patches upgrade the module `Aws.Sqs.Commands.Message` to support the features from SQS API version 2012-11-05, notably long polling and message attributes. The module has been rewritten almost completely.

*The changes are not backward compatible*. New parameters are added to the commands `SendMessage` and `ReceiveMessage` and new fields are added to the `Message` datatype. The API version for all SQS commands is set to 2012-11-05.