Feature request: periods with a 'human' interval #188

Many interval / periods are determined by business requirements. So for example "run this at every first monday of the month at 9.00am UTC" or "last friday of the month . At the moment this is impossible to do with pendulum (or with croniter for that matter).

So I would like to suggest a new feature that enabled this. I'm just not sure how to name it ;-).