Represent recurrent events

[propensive]

It should be possible to represent recurrent events which repeat periodically

It should support repetition with multiples of:

• annually
• monthly
• weekly
• daily
• hourly
• minutely
  where the repetitions are determined by,
• at a numbered second in a minute
• at a numbered minute and second in an hour
• at a given time in a day
• on a given day each week
• on a given date each month
• on a given week and day each month
• on a given week number and day each year
• on a given date each year
• on a given week in a given month each year

Combinations of these should most scenarios, though others may remain...

[propensive]

This should be based on the ISO 8601 standard, rather than creating our own.