Added encoding-type support to S3.

What it says on the tin. Adds the ``encoding-type`` parameter to:

* http://docs.aws.amazon.com/AmazonS3/2006-03-01/API/RESTBucketGET.html
* http://docs.aws.amazon.com/AmazonS3/2006-03-01/API/RESTBucketGETVersion.html 
* http://docs.aws.amazon.com/AmazonS3/2006-03-01/API/mpUploadListParts.html
* http://docs.aws.amazon.com/AmazonS3/2006-03-01/API/mpUploadListMPUpload.html

Review please? @danielgtaylor