Added new package_ensure parameter, and changed "ensure" parameter to "enable" parameter.

I will understand if you reject this pull request in its current form. 

I have a specific requirement to ensure a particular version of sudoers. In most modules, this parameter is called "package_ensure".

I've added this function and removed the autoupdate parameter. (if someone wants the latest version of sudoers, they should set package_ensure => 'latest')

The "ensure" parameter is ambiguous. For now I've renamed it to "enable" as a bool, and used that to purge configs or not. It does not remove the package too, as I would expect that to use the package_ensure => absent, purged, or whatever.

This allows maximum flexibility for users, and allows me to use this in my particular environment.