Function fill 

pub fn fill(
    path: &Path,
    only: Option<&HashSet<String>>,
    apply: bool,
    ask: Ask<'_>,
    jobs: usize,
    now: i64,
) -> Report

Give facets to the lessons of the store at path that have none (latest version), limited to only when given. A dry run (apply false) asks nothing and writes nothing. With apply, jobs calls at a time; each lesson with facets is appended as a new line of the same id and version (readers keep the latest line), its question, consequence and every other field unchanged, unless the lesson changed in the store meanwhile. After 3 failures without a success the run stops asking.