March Updates

Major changes:

• A class SIFile has been added to enable automatic formatting of output files. This is a work in progress.
• cctk.Molecule.to_string() and cctk.Molecule.from_string(string) now permit storage of cctk.Molecule objects. Part of the string is yaml-formatted, but most is not very human-readable (compressed ndarray bytes).

Minor changes:

• velocities can now also be generated from cctk.quasiclassical to initialize quasiclassical MD trajectories.
• charge and multiplicity have been added to cctk.XYZFile. Thanks to Gabe Gomes for pointing out this mistake.
• A new function compute_mass_spectrum has been added to cctk.helper_functions, and the mass spec backend from cctk.Molecule has been moved there.
• A new function cctk.Molecule.equal() has been added to allow for comparison of molecules.
• A bug in cctk.optimize has been fixed. Thanks to Gabe Gomes for pointing out this mistake.