Add option to output ISO 8601 format datetimes

[kinghuang]

Bottled Water outputs datetimes as a dict of datetime components like the following.

"created": {
  "DateTime": {
    "year": "2017",
    "month": "03",
    "date": "14",
    "hour": "15",
    "minute": "42",
    "second": "49",
    "micro": "230990"
  }
}

It would be handy to have an option to output an ISO 8601 combined date and time format instead.

2017-03-14T15:42:49.230990