• Add CookieStore trait to customize the type that stores and retrieves cookies for a session.
• Add cookie::Jar as a default CookieStore, easing creating some session cookies before creating the Client.
• Add ClientBuilder::http2_adaptive_window() option to configure an adaptive HTTP2 flow control behavior.
• Add ClientBuilder::http2_max_frame_size() option to adjust the maximum HTTP2 frame size that can be received.
• Implement IntoUrl for String, making it more convenient to create requests with format!.