Implementation of the set_output() API from scikit-learn. This means that now you specify the output of the chemotools methods to be either a numpy.ndarray or a pandas.DataFrame. The implementation follows the same framework as the scikit-learn (https://scikit-learn.org/stable/auto_examples/miscellaneous/plot_set_output.html). The default output is a numpy.ndarray. To change the output to a pandas.DataFrame you have to set set_output(transform='pandas') before calling any method.