Make the by parameter in feature_extraction.Agg and feature_extraction.TargetAgg to be optional, allowing to calculate aggregates over the whole data.
Removed feature_extraction.Lagger and feature_extraction.TargetLagger. Their functionality can be reproduced by combining feature_extraction.Agg and stats.Shift.
feature_extraction.Agg and feature_extraction.Target now have a state property. It returns a pandas.Series representing the current aggregates values within each group.