Openfisca-country-template

* Technical improvement
* Details:
- Adapt to version `15.0.0` of Openfisca-Core.
- Rename Variable attribute `url` to `reference`.

* Tax and benefit system evolution.
* Details:
- Allow to declare a yearly amount for `salary`.
- The yearly amount will be spread over the months contained in the year.

* Technical improvement.
* Details:
- Make `make test` command not ignore failing tests.

* Technical improvement.
* Details:
- Upgrade OpenFisca-Core:
- Update the way we define formulas start dates and variables stop dates.
- Update the naming conventions for variable formulas.
- See the [OpenFisca-Core Changelog](https://github.com/openfisca/openfisca-core/blob/master/CHANGELOG.md#1400---522).

* Tax and benefit system evolution.
* Impacted periods: from 2013-01-01.
* Impacted areas:
- Reform: `modify_social_security_taxation`.
* Details:
- Add a reform modifying the brackets of a scale:
- Show how to add, modify and remove a bracket.
- Add corresponding tests.

* Tax and benefit system evolution.
* Impacted periods: all.
* Impacted areas:
- `benefits`.
- `demographics`.
- `housing`.
- `income`.
- `taxes`.
* Details:
- Build the skeleton of the tax and benefit system.

Example Entry