• Add ClientBuilder::use_sys_proxy() to enable automatic detect of HTTP proxies configured on the system.
• Add ClientBuilder::no_proxy() to disable system proxies. This is the default for 0.9, but will change to detecting system proxies by default in 0.10.
• Add support for streaming request bodies in the async client.
• Add async::Response::text() that returns a Future of the full body decoded to a String.
• Add Clone for Certificate.