.flake8, .gitignore, LICENCE.txt, pyproject.toml
    New files

stoichiometry.py
    Reformatted to be PEP-8-compliant

stoichiometry.Stoichiometry.iter()
stoichiometry.stoichiometrize_species()
stoichiometry.vectorize_atoms()
stoichiometry.list_all_elements()
stoichiometry.project()
    Added doctests

stoichiometry.get_elements_counts()
    Removed legacy method

stoichiometry.Stoichiometry.all_atoms()
    Fixed broken doctest