Properly document the align argument – the function accepts “center” rather than “middle”. (#28)
Fixed an issue where empty fills were not handled correctly.
The interface has now been standardized such that each implemented window function has version center-aligned by default (e.g. roll_mean()), a left-aligned version (roll_meanl()), and right-aligned version (roll_meanr()).
Implement rolling window functions for mean(), median(), min(), max(), prod(), sum(), sd() and var().