v0.2.12

• Allow modeling of unobserved groups using aggregated data. The previous behavior was to drop rows in aggregate_data indicating zero trials. (They don't represent item responses.) Preserving them has the effect that unobserved groups, defined partially or entirely by the values of the grouping variables in zero-trial rows in aggregate_data, can be included in a model.
• Fix an unexpected error when 1) aggregate_data is used without item_data, 2) no demographic groups are specified via group_names, and 3) geographic modifier_data is used.
• Fix the check for missing modifier_data. Geographic modifier_data must cover all combinations of the geo and time variables in the item response data (individual or aggregated), but because of a bug in the validation of the geographic data, this requirement was not always enforced. In some cases a warning would appear instead of an error.