message: Use 'avg' for all data types and results + list
diff: @@ -551,7 +551,7 @@ util::Optional<Mixed> Results::sum(ColKey column)
  util::Optional<double> Results::average(ColKey column)
  {
  size_t value_count = 0;
  - auto results = aggregate(column, "average", [&](auto&& helper) {
  + auto results = aggregate(column, "avg", [&](auto&& helper) {
  return helper.avg(column, &value_count);
  });
  return value_count == 0 ? none : util::make_optional(results->get_double());
  