Add example script to prepare the datasets used for HPO

prepare_data.py

+# Used to prepare the example datasets for hyper-parameter optimisation
+
+import numpy as np
+
+np.random.seed(123)
+import cmlkit
+
+data = cmlkit.load_dataset("nmd18_train")
+
+rest, train, test = cmlkit.utility.threeway_split(data.n, 800, 200)
+
+train = cmlkit.dataset.Subset.from_dataset(data, idx=train, name="nmd18_hpo_train")
+print(train.n)
+train.save(directory="data/cmlkit")
+test = cmlkit.dataset.Subset.from_dataset(data, idx=test, name="nmd18_hpo_test")
+print(test.n)
+test.save(directory="data/cmlkit")