code: function off (state, eventName, handler) {
    if (arguments.length === 2) {
      state.emitter.removeAllListeners(eventName)
    } else {
      state.emitter.removeListener(eventName, handler)
    }
  
    return state.api
  }
docs: unbinds event from handler
  
  @param  {String} eventName   push, pull, connect, disconnect
  @param  {Function} handler   function unbound from event
  @return {Promise}