Nice to have: Rename twodfdr classes to have consistent capitalisation and meaning
e.g. if we keep TdfArgs, then Tdfio should be TdfIo. Alternatively, if we keep Tdfio, then we should use Tdfargs.
e.g. if we keep TdfArgs, then Tdfio should be TdfIo. Alternatively, if we keep Tdfio, then we should use Tdfargs.