code: function listDepsForBook(book) {
      var config = book.getConfig();
      var plugins = config.getPluginDependencies();
  
      return listDependencies(plugins);
  }
docs: List all plugin requirements for a book.
  It can be different from the final list of plugins,
  since plugins can have their own dependencies
  
  @param {Book}
  @return {List<PluginDependency>}