Function write_list 

pub fn write_list(
    config_path: &Path,
    path: &str,
    wanted: &[String],
    shipped: &[String],
) -> Result<(), String>

Writes a list’s changes so that it holds wanted, compared with what the packs alone give (shipped): the words not shipped go to add, the shipped ones not wanted to remove. Wanting the shipped list takes the changes out. A named list (MAPS) is not written here: see write_names.