APIs for loading dataset and models

[shelllbw]

• A load_dataset() function that could load pre-built datasets for a specific X-ray absorption edge, e.g. load_dataset('fe') would load the iron (Fe) dataset of (X, y) values for iron-containing molecules. These prebuilt datasets would probably be stored as .npz archives (or possibly HDF5 archives if they eventually became large enough!).
  Example: https://scikit-learn.org/stable/modules/generated/sklearn.datasets.load_iris.html

• A XANESNET object or load_xanesnet() function that returns the 'canonical' pre-trained XANESNET model.
  Example: https://www.tensorflow.org/api_docs/python/tf/keras/applications