Omitting repetition ending date

[ShoresOfNowhere]

Sometimes it can be useful to omit the repetition ending date if printing a human readable string, so I added this option.

[rlanvin]

Hello, thanks for the PR. Technically it looks good, but I'm trying to understand the use case, and why you need a different option than the (already existing) include_until. I'd like to avoid including too many specific options, that could lead to confusion. Could you elaborate in what case include_until is not sufficient for you?

[ShoresOfNowhere]

The point is that turning off include_until will omit the entire until part, while in my use case it would remain VERY useful that until is shown if it's forever or other particular endings; it's simply not shown if it's a simple specific date as it's normal...

That stems from the fact that in the DB I need to have the repetition ending date as a separate field (that surely gets inserted in the RRULE while using your library) as it permits me to prune very efficiently the events to be considered for a specific time period, as I can set some WHERE conditions on the starting, ending and repetition ending dates.

This in turn would mean that if the repetition ending date is something "special" such as forever, this is would NOT be clarified by the empty repetition ending date field, and thus is very useful that is expressed by the RRULE human readable label, while if the repetition ending date is simply set to a date, the human readable form of the RRULE would be uselessly repeating the date shown in the side by side rep ending date field, using valuable screen estate that can be used in other interface elements.

But I understand that you could not like my specific use case, I just thought it might be useful for everybody. :)