Merge all true table into single excel file.

def merge_true_table():
    """Merge all true table into single excel file.
    """
    writer = pd.ExcelWriter("True Table.xlsx")
    for p in Path(__file__).parent.select_by_ext(".csv"):
        df = pd.read_csv(p.abspath, index_col=0)
        df.to_excel(writer, p.fname, index=True)
    writer.save()