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Features:
- `gama.__version__` can now be used to retrieve gama's version.
- `fit_arff`, `score_arff` and `predict_arff` now accept a `target_column` parameter to specify the target.
If left unset, the last column of the ARFF file is assumed to be the target column.
Bugfixes:
- fit(x, y) may now be called with y as (N,1) array.
- ensemble post-processing is now compatible with non-zero indexed class labels
Maintenance:
- `__version__.py` is now the only place with hard-coded version.