What this PR brings
An exciting but under-documented feature, "axes", now has much better test coverage and thus long-term maintainability (the documentation is still lacking, but see https://github.com/openfisca/tutorial for demos)
Breaking changes
This PR deprecates the `new_scenario` approach to constructing Simulation objects. This will impact you if:
- your notebooks or scripts or other Python code rely on the France model and use the old form of creating a Simulation object (see below)
- **or** your country package defines a Scenario class and injects it [the way France does](https://github.com/openfisca/openfisca-france/blob/11b18985ce4decc31b5666114b2525dddf42652b/openfisca_france/france_taxbenefitsystem.py#L29)
**To migrate to this version**, if you are in the first case, the minimum required change is this:
*The old way:*
simulation = tax_benefit_system.new_scenario().init_single_entity(...some data...).new_simulation()
*The new way:*
At the top of your file
from openfisca_france.scenarios import init_single_entity
Below
simulation = init_single_entity(tax_benefit_system.new_scenario(), ...some data...).new_simulation()
If you are in the latter case, you must also transform your `init_single_entity` from a Scenario method to a regular function at global scope, and change your tests and reuses as described above.