• added: Add WebSocket::protocol to return the selected WebSocket subprotocol, if there is one. (#1022)
• fixed: Improve error message for PathRejection::WrongNumberOfParameters to hint at using
  Path<(String, String)> or Path<SomeStruct> (#1023)
• fixed: PathRejection::WrongNumberOfParameters now uses 500 Internal Server Error since
  it's a programmer error and not a client error (#1023)
• fixed: Fix InvalidFormContentType mentioning the wrong content type