Add make clean target
Add make clean target

SophieIPP/openfisca-france,adrienpacifico/openfisca-france,sgmap/openfisca-france,adrienpacifico/openfisca-france,benjello/openfisca-france,benjello/openfisca-france,antoinearnoud/openfisca-france,sgmap/openfisca-france,antoinearnoud/openfisca-france,SophieIPP/openfisca-france