Develop

This branch introduces several new features of three different branches in my fork:

* `destination_subfolder`
  * adds the possibility to put the backups into a subfolder of the destination filesystem.
  * adds the possibility to use a already mounted filesystem as destination (config: `mount_dest_device`)
  * cleans the code a little according to ruby styleguides
  * adds more comments to the config and sources samples
  * fixes several double slashed path problems
* `inclusions` adds rsync `--include` option support to sources file
* `allow_backup_root` creates a `root` subdirectory if you have root as a source