Customizing name and even folder for backups.

I think it is great greed saves backups of files it overrides. But I would like to be able to customize the file name. It would be specially useful to be able to use .filename.bak.0, so that the file is hidden. Let's agree on config syntax.

<pre>
backup {
    folder = '' 
   #  (folder would be inside codeRoot)
    filename = "${GeneratedFileName}.bak.${BackupNum}"
}

</pre>
This reuses the GeneratedFileName that is used for after gen hooks.