Support chunked transfer encoding as an additional way of streaming

[amazeika]

We currently support Range Headers through our stream transport. Problem is that this mechanism is problematic with servers sitting behind a proxy.

The idea would be to support chunked transfer encoding in our stream transport as a way to properly stream files without having to worry about proxies. Streaming should just work.

See also: https://www.sitepoint.com/php-streaming-output-buffering-explained/

[johanjanssens]

@amazeika Also useful: https://gist.github.com/CMCDragonkai/6bfade6431e9ffb7fe88