Consider addition of EpiWeek

[sadiekelly]

Timing of reports is currently captured using date_report (date case first included in a situation or other report).
Would it be useful for aggregation purposes to collate these into EpiWeeks? I understand EpiWeek definitions differ by country, so we could make our standard definition depending on the date_report (OpenDengue has a similar approach to standardise to a universal date format).

[abhidg]

We will document this functionality: in R, use lubridate::isoweek() or lubridate::epiweek(); for Python, use epiweeks package