Openfisca-country-template

* Minor change.
* Details:
- Update links to the doc.

* Minor change.
* Details:
- Document housing tax.

* Technical change.
* Details:
- Tests library against its packaged version.
- By doing so, we prevent some hideous bugs.

> Note: Version `3.5.1` has been unpublished as it accidentally introduced a bug. Please use version `3.5.2` or more recent.

* Technical change.
- In the `/spec` Web API route, use examples that apply to this country package.

* Tax and benefit system evolution.
* Impacted periods: all.
* Impacted areas: `housing`.
* Details:
- Introduce `code_postal` variable.

* Minor change.
* Details:
- Update entities labels.