Add support for backing up parts of the Filesystem

There are easy ways to backup parts of the filesystem using normal unix commands and cron, but I think adding this functionality to this module would make it really robust and useful for non-coders. I'm mostly interested in this functionality for backing up a site's files directory after it's gone into production, but it could be useful for backing up the entirety of the Drupal directory or just important pieces too.

It would be nice to have this functionality present in the module itself rather than in outside shell scripts, so that it can be easily configured for a site without writing/rewriting scripts for every new site.