Ensure that sum_by_entity doesn't generate an array of booleans and that any_by_roles generates an array of booleans.
Move statshelpers to openfisca-(country)-data projects.
By defaut, in debug mode, log only formula calls with non-default parameters. Add debug_all mode.
Add support for formulas traceback.
Merge branch 'master' of https://github.com/openfisca/openfisca-core