Suggestion: Header for thermo.out file

[erhart1]

It would be useful to include a header in the thermo.out file that specifies the meaning of the columns. If these lines are prepended by a widely used comment symbols (e.g., #), the user experience should be (hopefully) unaffected. At the same time it would help users (and parsers) to read the content of the file. This would in particular improve readability/interpretability if the number of columns/data changes, e.g., when switching from an orthorhombic to a triclinic cell. Finally, this would also be useful if one were to decides to add more information to this file in the future.