Openfisca-tunisia

* Add 2017 references to `impot_revenu.bareme`

* Move tests outside `openfisca_tunisa` module
* And delete `old_tests`
* Move PDF and Excel files from repository to public drive
* Update README with public drive link and API latest information
* And delete old `api/` configuration

* Add continuous integration with CircleCI v2
* Add `CONTRIBUTING.md` information

* Update `smig` variable type
* Add parameters on `SMIG` _components_
* `cotisations_sociales/gen/salaire_de_base_40h_horaire.yaml`
* `cotisations_sociales/gen/salaire_de_base_40h_mensuel.yaml`
* `cotisations_sociales/gen/salaire_de_base_48h_horaire.yaml`
* `cotisations_sociales/gen/salaire_de_base_48h_mensuel.yaml`
* `cotisations_sociales/gen/indemnite_complementaire_provisoire.yaml`
* `cotisations_sociales/gen/majoration_smig_40h_mensuel.yaml`
* `cotisations_sociales/gen/majoration_smig_48h_mensuel.yaml`
* Update parameters and references on `SMIG`
* `cotisations_sociales/gen/smig_40h_horaire.yaml`
* `cotisations_sociales/gen/smig_40h_mensuel.yaml`
* `cotisations_sociales/gen/smig_48h_horaire.yaml`
* `cotisations_sociales/gen/smig_48h_mensuel.yaml`
* Update parameters and references on `SMAG`
* `cotisations_sociales/gen/smag_journalier.yaml`

* Add `notebooks/test_notebooks.py` script to execute .ipynb files
* Add `Makefile` tag `nb` to test specified notebooks

* In `TypesRegimeSecuriteSociale` and `/parameters/cotisations_sociales`
* Rename `cnrps_sal` to `salarie_cnrps`
* Rename `cnrps_pen` to `pensionne_cnrps`