Added Hiera and source file support.

@jpds Is this correct? There's no changes to [init.pp](https://github.com/gds-operations/puppet-auditd/blob/master/manifests/init.pp) to support auto-enabling the hiera functionality - which I think means that's either been missed out of the PR, or the comment is incorrect and you should be including `auditd::rules` in your manifest.