code: function emit (msg, done) {
      var raw_data = [
        {source: 'demo-plugin', payload: {val: 1, tag: 'foo'}},
        {val: 2, tag: 'foo'}
      ]
  
      done(null, raw_data)
    }
docs: On interval, Vidi: Metrics will call all emitters and ask for data. Multiple points of data can be sent in a single emit.