• Add Response::text_with_charset() to allow setting the default charset to decode.
• Add Error::source() implementation.
• Add async::ClientBuilder::timeout() option, will timeout the connect, request, and response body futures.
• Fix gzip + chunked transfer encoding issue preventing connection reuse.
• Fix RequestBuilder::query() to not add just "?" if the encoded query is empty.
• Fix including new cookie headers when response is a redirect.