RTK v3 migration guide

Use --size instead of --dimension

As of RTK 3.0, the --dimension argument in applications is deprecated and will be removed in a future release. Please use the --size argument instead. This update aligns RTK with upstream ITK’s member name, where --size more accurately reflects the expected parameter (e.g., image size) and avoids confusion with spatial dimensions (e.g., 2D vs 3D).

Forbild phantom file format only

The legacy rtk::GeometricPhantomFileReader has been removed starting with RTK 3.0. This handcrafted file format was not documented and everything it could do is also achievable with the only file format for geometric phantoms accepted in RTK 3.0, the Forbild phantom file format. The flag --forbild has also been removed from command line tools as it is now the default and only option.