Add a test showing how to use new functions and decorators to declare reference input variables and a reference formulas, using a better syntax than build_column... functions.
Add a test showing how to use new functions and decorators to declare reference input variables and a reference formulas, using a better syntax than build_column... functions.

benjello/openfisca-core,openfisca/openfisca-core,benjello/openfisca-core,openfisca/openfisca-core,sgmap/openfisca-core,adrienpacifico/openfisca-core