S3Proxy 1.9.0

• add alias bucket middleware #363
• add sharded bucket middleware #325 #351
• allow mapping buckets to different storage backends #378
• fix ETag with multipart upload using transient storage backend #338
• handle possibly-missing Content-Length #357
• optimize GetBlob with Range header when using transient storage backend
• support Iso8601 in date headers #366
• upgrade to Apache jclouds 2.4.0 with several storage backend compatibility fixes
• upgrade to Jetty 9.4

Thanks @kortemik, @peterzeller, and @timuralp for opening pull requests to improve S3Proxy!