* Some fraction of the codebase gets proper docstrings, documentation is changed so it allows for testing.
* All the states-related code gets refactored to a `pyvalem.states` subpackage. As a result, if the concrete state classes need to be imported on their own, this is done now by
from pyvalem.states import AtomicConfiguration
from pyvelem.states import MolecularTermSymbol
etc.