Changes in version 0.1.0                        

  - Initial release.
  - Added maxtwin() for deterministic train/test splitting with
    distribution preservation and train/test separation.
  - Added initialmaxtwin() for the Step 1 split without the iterative
    separation improvement.
  - Added input validation, examples, and test coverage for
    deterministic output, split sizes, paired data, and high-dimensional
    inputs.
  - Added Helmert coding for factor predictors and factor responses.
  - Added predictor-only splitting when Y is omitted.