v0.4.0

• Breaking: Drop the io-stream dependency. Stream.new and Stream.open no longer coerce or wrap their input and output arguments; raw IO objects are used as-is. Callers that relied on stream.io returning an IO::Stream::Buffered should wrap the IO themselves before passing it in.
• Simplify Stream#read to delegate directly to the underlying input, since the HTTP/2 framer always requests exact byte counts (header size, then payload length).