ENH: rolling for periodic data
#### Is your feature request related to a problem?

I have a periodic DataFrame and I would like to compute a rolling mean. However, I struggled to do this with pandas nicely. What I ended up dooing was to copy the tail of the DataFrame to the top and the head to the bottom, and than used DataFrame.rolling().

#### Describe the solution you'd like

It would be nice to have somthing like `DataFrame.rolling(how='periodic')`

#### Describe alternatives you've considered

I am not sure how many users need this feature, so it might not be worth adding it for the few needing it.