Hipe4ml

- Allowing writing data frames inside tree handlers into ROOT files
- Bumping the dependency tree
- Docs cleanup

- Various fixes for consistency and reproducibility of the analyses
- Fix a casting issue in the bayesian optimisation routine
- Improved TreeHandler: reads multiple files + return new TreeHandler when performing not in place operations
- Bump packages in the dependency chain (notably XGBoost 1.0.x, waiting for shap to move to 1.1.x)
- Tests, tests and tests added (and more to come)

- Added the TreeHandler utility to read and handle trees from root files or pandas from parquet files
- Various fixes to the plotting utils

- Fix probability prediction in case of multi-class classification
- Fix uncertainties in normalised bdt output distributions
- Add one-vs-one option for ROC curves and ROC AUC score in multi-class classification
- Skip 0.0.4 to fix the doc generation

- Support bayesian optimization with multiclass discriminators
- Add documentation generation
- Several fixes to the plotting utilities

- Add support for multi-classification problems
- Various fixes to the plotting code