Feature calculator return type documentation

[dilwong]

This isn't a bug, but more of a documentation issue. According to the docs, as well as in the docstrings for the functions in tsfresh.feature_extraction.feature_calculators, the documented return type for feature calculators of fctype=combiner appears to be incorrect. For example, see agg_linear_trend that claims to return a pandas Series, or augmented_dickey_fuller that claims to return a float.

[nils-braun]

Very good observation @dilwong (and sorry for the late response). Would you like to do a PR to fix this (or at least some of them)?

[dilwong]

Ok sure, I submitted PR #1070 for this.