code: func (o *ClientOptions) SetStore(s Store) *ClientOptions {
  	o.Store = s
  	return o
  }
docs: // SetStore will set the implementation of the Store interface
  // used to provide message persistence in cases where QoS levels
  // QoS_ONE or QoS_TWO are used. If no store is provided, then the
  // client will use MemoryStore by default.