Add new params and full hiera support

This adds 3 new params and full Hiera support.
$packages which allows overriding the package list 
$rules which allows specifying a hash of logrotate rules
$hieramerge which allows hiera hash merging of logrotate rules

I've also updated the rspec tests and cleaned up the code some for a bit more standard behavior (init.pp).

This SHOULD be backwards compatible with existing usage.