message: Corrected some over use of StlVecType 3
diff: @@ -1139,7 +1139,7 @@ template<typename T, typename I_V, typename ... Ts>
  DataFrame<I, H> DataFrame<I, H>::
  groupby1(const char *col_name, I_V &&idx_visitor, Ts&& ... args) const {
  - const StlVecType<T> *gb_vec { nullptr };
  + const ColumnVecType<T> *gb_vec { nullptr };
  if (! ::strcmp(col_name, DF_INDEX_COL_NAME))
  gb_vec = (const ColumnVecType<T> *) &(get_index());
  @@ -1187,8 +1187,8 @@ groupby2(const char *col_name1,
  I_V &&idx_visitor,
  Ts&& ... args) const {
  - const StlVecType<T1> *gb_vec1 { nullptr };
  - const StlVecType<T2> *gb_vec2 { nullptr };
  + const ColumnVecType<T1> *gb_vec1 { nullptr };
  + const ColumnVecType<T2> *gb_vec2 { nullptr };
  if (! ::strcmp(col_name1, DF_INDEX_COL_NAME)) {
  gb_vec1 = (const ColumnVecType<T1> *) &(get_index());
  @@ -1255,9 +1255,9 @@ groupby3(const char *col_name1,
  I_V &&idx_visitor,
  Ts&& ... args) const {
  - const StlVecType<T1> *gb_vec1 { nullptr };
  - const StlVecType<T2> *gb_vec2 { nullptr };
  - const StlVecType<T3> *gb_vec3 { nullptr };
  + const ColumnVecType<T1> *gb_vec1 { nullptr };
  + const ColumnVecType<T2> *gb_vec2 { nullptr };
  + const ColumnVecType<T3> *gb_vec3 { nullptr };
  if (! ::strcmp(col_name1, DF_INDEX_COL_NAME)) {
  gb_vec1 = (const ColumnVecType<T1> *) &(get_index());
  