extract-xiso compatibility mode

[antangelo]

Would be nice to have an extract-xiso compatibility mode so that xdvdfs can be used as a drop-in replacement in scripts/tooling.

At minimum should provide the main modes: -x, -l and -c. -r is a nice-to-have, but xdvdfs does not support that functionality natively yet. Options are also a nice-to-have.

Interface-wise, I have a couple ideas:

1. Support these flags at top level, such that swapping extract-xiso for xdvdfs in any command will work (e.g. extract-xiso -c bin can become xdvdfs -c bin). This can also be done by checking if the binary name is extract-xiso.
2. Add a extract-xiso subcommand that supports these flags, such that swapping extract-xiso for xdvdfs extract-xiso will work (e.g. extract-xiso -c bin can become xdvdfs extract-xiso -c bin).

I personally think that either the second option or checking the executable name is cleaner overall.