Add undocumented fields: calendarEvent

[tinovyatkin]

top-level:

barcodes: [],
calendarEvent: {
  "title": "Party",
  "location": "Discovery Meadow",
  "startDate": w3cdate
  "endDate": w3cdate
}

Source: https://developer.apple.com/videos/play/wwdc2018-720/?time=1705

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[alexandercerutti]

It will be documented soon along with other features.
Seems like Apple is working on an updated version of the documentation.
I can say that because I contacted Ben Chester on Twitter and asked him a few things.