Exponential weighted moving window statistics

[Chemcy]

It seems that pandas has not provided iterators for rolling/ewm functions, and your project is really nice structured. Maybe another base class is needed for iterators of ewm statistics.

[ajcr]

Thank you - this would be a great addition to the project. I'll need to look into ewm statistics some more, but your suggestion of a new base class to handle the necessary logic seems like a good approach.