Sync scheme headers

After editing scholia/scheme.yaml, run:

scholia update

This reads the question names from the scheme and updates the column headers in scholia/students.csv to match. By default the questions are sorted alphabetically. To keep the order they appear in scheme.yaml instead, pass the --preserve-order flag:

scholia update --preserve-order

Any question already in the CSV retains its data. Questions present in the CSV but absent from the scheme are appended after the scheme questions rather than removed, so no data is lost.

Typically, run scholia update once after the initial scheme is written, and again whenever a new question is added to the scheme.