S3Proxy 4.1.0

• Authenticate against Swift's tempauth as well as Keystone
• Fix ListObjectsV2 start-after on the azureblob backend, #938
• Handle conditional deletes natively on the aws-s3, filesystem, and transient backends
• Harden the SFTP host-key verification
• Speak AWS SDK request, response, and exception types across the storage backend interface
• Support object versioning on the aws-s3, google-cloud-storage, and transient backends, #74, #1136
• Support server-side encryption on the aws-s3, azureblob, and transient backends, #402

Thanks @gavin-thompson-postman for opening a pull request to improve S3Proxy!