~~~~~~~~~~~~~~~~~~
* Change the default number of estimators in causal regression forest from 100 to 2000
* Add validation to ensure the resulting records after taking sample fraction is always at least 1
* Change ``n_features_`` attribute to ``n_features_in_`` for consistency with sklearn
* Add validation to ``sample_weight``. Because of internal rng, this ensures that passing no weights is equivalent to passing a vector of ones
* Add validation to the number of features in the test set.
* Fitted estimators now hold a pointer to a C++ forest, eliminating the need for deserialization on predict which makes predictions faster
* Change the attribute name from ``grf_forest_`` to ``boosted_forests_`` on ``GRFBoostedRegressor``
* Add decision tree regressors for each forest type (except boosted)
* Add a ``GRFBaseTree`` class for shared methods on decision trees
* Add ``estimators_`` property to forests which return a list of tree estimators
* Add ``get_estimator`` method to forests to extract a single estimator
* Fix a bug on local linear forest where ``ll_split_variables_`` was not being set properly
* Add ``get_feature_importances`` to forests
* Add ``get_split_frequencies`` to forests
* Add ``get_kernel_weights`` to forests
* Add ``COPYING``, ``README.md``, ``REFERENCE.md`` source files from grf to package source files
* Remove leading underscore from all ``grf_forest_`` dictionary keys
* Implement most of the sklearn low-level ``Tree`` API into decision trees
* Add ``criterion`` (str) attribute to all estimators
* Remove arguments related to sparse data from bindings
* Update ``grf`` to 2.0, and update bindings
* Add ``GRFClassifier`` and ``GRFTreeClassifier`` estimators
* Change ``classes_`` and ``n_classes_`` to ``clusters_`` and ``n_clusters_``. ``classes_`` and ``n_classes_`` are now used for target classes in classification estimators
* Remove the ``DataNumpy.cpp`` class. This is no longer needed with the ``grf`` 2.0 updates to the ``Data.cpp`` class
* Rename the ``DataNumpy`` Cython class to ``Data``
* Remove extern cpp includes from Cython ``.pxd`` file and add ``cpp`` files to ``Extension``'s ``source`` arg
* Rename forest estimators to ``GRFForest...``