totalItems - is an approximate number of items in the user's entire history.
nextPageToken - is an opaque string you can use to get the next page of history.
It looks a lot like an ISO 8601 formatted date right now, but you should not count on that
being true. The nextPageToken will be present on all but the last page
long_url - items contains the list of entries for the first "page" of the user's history,
in order of descending creation time. The values for each entry are the same as specified in
the Analytics section
https://developers.google.com/url-shortener/v1/getting_started#url_analytics.