[Q/FR] Support for relative dates

Do you plan to support relative dates with a human readable instructions, like "last year" or "next month"... I would like to have something to parse these relative to today (or an argument passed in). But also it should understand input such as "2018" or "jan 2018" to give the specified intervals.

My current use-case is to make better reports for org-clock-budget where you could specify the intervals/periods with a simple query such as "last year" or "this week" and it will give you a report. This way users can view historical reports as well as the current ones.

It feels like it might be a separate package, "period" or something for returning the intervals specified by the query.

Edit: the inspiration comes from ledger https://github.com/ledger/ledger/blob/7c0ae5b02571e21f97d45f5d091cb78af9885713/src/times.cc and how it handles relative times. Maybe I will try to port it using ts as a backend.