AWS S3 support

[eshaan7]

First off, kudos for the awesome work.

Is there a way to use this with S3 bucket ? Something like a CDN server.

Example flow:

1. When user goes to:

http://localhost/path/to/s3/file.jpg?width=100&height=200

2. The server then downloads the file from S3, applies the given transformations and outputs the final image's buffer in response.