2.3.1

• Refactor (phase diagram) facet to (chemical potential) limit in doped chemical potential
  functions, as this is more intuitive for most users.
• Tests updates.
• Minor efficiency/verbosity/robustness/docs improvements.
• Update default KPOINTS for convergence/production runs in chemical_potentials based on testing.
• Add optional projections of site displacements upon given vectors by @ireaml