code: public static List<CommentTreeElement> flattenCommentTree(List<CommentTreeElement> commentTree) {
          List<CommentTreeElement> target = new ArrayList<CommentTreeElement>();
          flattenCommentTree(commentTree, target);
          return target;
      }
docs: Flatten the comment tree.
  The original comment tree is not overwritten.
  
  @param cs        List of comments that you get returned from one of the other methods here
  
  @return    Flattened comment tree.