future warnings

[solegalli]

List of future pandas warnings

c:\users\sole\documents\repositories\feature_engine\feature_engine\creation\math_features.py:212: FutureWarning: The provided callable <function sum at 0x0000016E1CA6D090> is currently using Series.sum. In a future version of pandas, the provided callable will be used directly. To keep current behavior pass 'sum' instead.

[glevv]

Connected to this
pandas-dev/pandas#53425

I think we can easily suppress this warning or not so easily bump pandas version.

We should also add information to this transformer, that same numpy and pandas functions could lead to different results (this is why they raise this warning). For example, np.std has ddof=0 while Series.std() has ddof=1