- Reject connections if RSV is not equals to `0`.
 - Validate close reasons to be valid UTF-8 if UTF-8 validation has been requested.
 - Accept zero-length frames starting a message.
 - Deliver stored messages correctly if they're immediately followed by a close.
 - Reject continuations if there's no started message.
 - Disable streaming for frames. A single frame is now always buffered. A message can still be streamed via multiple frames.