2019-08-02 Breaking change: Fix wakeup stream if connection closed externally

• BREAKING CHANGE: Fix: Correctly wake up tasks waiting for a next message if the connection gets closed externally.
  This prevents these tasks from hanging indefinitely.
  As a consequence, WsStream::close now returns a Result, taking into account that if the connection is already
  closed, we don't have the CloseEvent. Instead a WsErr of kind WsErrKind::ConnectionNotOpen is returned.
• update to async_runtime 0.3