value_col and transform_value_col supports fully only one value #60
Description
value_col and transform_value_col supports fully only one value. When more values are passed ( e.g. "value", "lower", "upper"), support of all functions are not guarenteed. Support of this functionnality should be offered and implemented throughout the package's functions.
This would also mean reviewing some assert_ assumptions on the data quality (assert_data_calculation_hep(), etc.) and presence (e.g. assert_iso3_not_empty(), xmart_col_types(), xmart_cols(), etc.) to allow for value_col with only NAs as values should not be always expected.