4.0.0 RC7

Note: This is a pre-release, there might be breaking changes in the final stable version.

• Added HttpClient interface and HttpClientBuilder, use these instead of the previous Client class
• Added gzip bomb protection (#208)
• Added Request::removeAttributes()
• Added ConditionalInterceptor / IfOrigin interceptor
• Added Response::getOriginalResponse()
• Added optional $body parameter to Request::__construct()
• Allow null return in ModifyRequest / ModifyResponse
• Drop content-encoding header on decompression (#207)
• Use pings to test HTTP/2 connection liveness
• Improved request cloning
• Disallow user info in URIs by default
• Validate response protocol version
• Assign default reason phrase if none is provided
• Removed Response::setReason(), use Response::setStatus() with its second parameter instead