- update `fkooman/rest` and update code for API changes
- `CertService` now extends `Service` so all calls are not implemented
  in `CertService` and not in the `api.php` script
- path changed from `/api.php/` to `/api.php/config/` for generating and
  deleting configurations (CRL path unchanged)
- the POST request now expects the commonName in the POST body, not in the
  URI, see `README.md` for updated `curl` examples
- implement Basic Authenication (issue #4)