Sigv4 support for S3 by lindsley
Fixes to get BJS working - hacks!
S3 domains are a wee bit non-standard between regions.

Just a bit.
Updated Elasticache to utilize SigV4.
Added conditional use of SigV4 to EC2.
Initial version of BigMessage.
Fix doc string.
Fix some doc strings and add comments.
Fixing docstring.
Updated the Support API to current, including some previously required parameters becoming optional.
Added conditional signing selection to S3.
Added notes about multipart uploads to S3.
Added encoding-type support to S3.
Delete S3 object first, then SQS message.  Raise an exception if unable to decode s3_url.
Added missing docs.
Merge branch 's3-encoding-type' into develop
Merge branch 'elasticache-sigv4' into develop
Merge branch 's3-mp-notes' into develop
Merge branch 'ec2-bjs' into develop
Merge branch 's3sigv4' into develop