2.4.2

• Allow cases where the calculated host material is unstable wrt competing phases (above the hull), by downshifting to the hull and warning the user about this.
• General updates to chemical potentials code; more robust (better error catches and messages, API key handling), more informative, cleaner outputs.
• Updates to match recent changes in pymatgen object types (e.g. #68)
• Minor efficiency & robustness updates