convenience methods to set/add DataFrame to table.data

[jorahn]

table.append(df)
def append(rows):
    if isinstance(rows, pd.DataFrame):
        rows = rows.to_dict('records')
    # ...

table.data = df
def _set_data(self, data):
    if isinstance(data, pd.DataFrame):
        data = data.to_dict('records')
    # ...