S3Proxy Files

• Answer binary/octet-stream for an object stored without a Content-Type, [#179]
• Build Docker image on a custom JRE, [#401]
• Copy multipart parts server-side when possible, [#76]
• Evaluate the policy a form POST is signed against, [#73]
• Join multipart parts with copy_file_range on the filesystem backends, [#471]
• Remove Apache jclouds and the Atmos and B2 storage backends
• Perform conditional PutObject natively where a backend supports them and refuse where it cannot, [#627], [#894]
• Reuse Azure client across multi-part uploads to avoid reauthentication, [#1104]
• Report the Azure ETag under a composite suffix, [#335], [#555], [#650], [#724]
• Return and persist flexible checksums, [#656]
• Support POST upload policies, [#73]

Thanks @aldrinjenson and @toindev for opening pull requests to improve S3Proxy!