SNS to SQS messages only work with raw message delivery. #175

It seems like this library only works for messages sent from SNS that are sent as raw messages. if your subscription is not sending messages as raw, the messages come through wrapped in a "standard" json format where you message body is one of the fields in the json. the original SNS message attributes are also not put into the SQS message attributes. This means that the message is not unpacked and you have to upcak the message manually after the receive message request is finished, which defeats the whole purpose of this library. is there a suggested way to unpack messages from S3 that are sent this way? or do i need to always use "raw message delivery" for all of my messages?