Sqs.Core: add comments to constructors of MessageAttribute
Sqs.Core: derive some standard type classes for some types
Sqs.Commands.Message: reimplementation with support for SQS version 2012-11-05 features
add test suite for SQS
Merge pull request #113 from alephcloud/SQS-2012-11-05

Update of SQS to API version 2012-11-05