Added Full ZFS Dataset Support:

- The script will now create a ZFS dataset for each jail if the 'jailmaker' directory is a ZFS dataset
- The script will create the 'jails' directory as a dataset if the 'jailmaker' directory is a ZFS dataset
- The script will now remove the ZFS dataset (including snapshots) when deleting the jail
- Dual mode: For legacy use without datasets, it will continue to work as previously

Added a guide to migrate from using directories to using ZFS datasets.

Closes #80.

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Co-authored-by: Jip-Hop <2871973+Jip-Hop@users.noreply.github.com>