[Feature Request] Support for more granular recurrence

[pluma9]

In many situations, a task does not have to be repeated exactly every week, month, etc. For example:

• perform dental checkup every 3 weeks
• write a report every 4 days.

Having a way to specify more granular recurrence will be helpful in many real life use cases.

I think we can have something like this:

ultralist add write report recur:4days

We can always use days and not use months or years to simplify things.