pt.debug utility transformers

[cmacdonald]

Is your feature request related to a problem? Please describe.
I'm always frustrated when I cant figure out what the intermediate output in terms of data, or columns are, for a given transformer

Describe the solution you'd like
Utility transformers that can be inserted, namely:
pt.debug.print_rows()
pt.debug.print_columns()

Initial implementations

def print_columns(by_query=True, message=None):
    def _do_print(df):
        if message is not None:
            print(message)
        print(df.columns)
        return df
    return pt.apply.by_query(_do_print) if by_query else pt.apply.generic(_do_print) 

def print_rows(by_query=True, jupyter=True, head=2, message=None, columns=None):
    def _do_print(df):
        if message is not None:
            print(message)
        render = df if head is None else df.head(head)
        if columns is not None:
            render = render[columns]
        if jupyter:
            from IPython.display import display
            display(render)
        else:
            print(render)
        return df
    return pt.apply.by_query(_do_print) if by_query else pt.apply.generic(_do_print)