Hiera support

Dear,

I added support for Hiera.  With these changes it is possible to do the configuration fully in hiera.  I also extended the documentation to show an example using hiera (in fact it will give the same result as the manifests example).

No tests are in this pull request, nothing is changed so tests should keep succeeding.  Honestly I don't know how to test hiera capability of a module.

I hope this can be pulled in, feedback is welcome.

Kind regards,