fastdid - Fast Staggered Difference-in-Difference Estimators

A fast and flexible implementation of Callaway and Sant'Anna's (2021)<https://www.sciencedirect.com/science/article/pii/S0304407620303948> staggered Difference-in-Differences (DiD) estimators and its extensions, fastdid reduces the computation time from hours to seconds, and incorporates extensions such as time-varying covariates and multiple events.