Commenting.
nomis-dirtree: Use `save-selected-window`.
nomis-dirtree: Use `let*`, not `let`, as your "default".
nomis-dirtree: Add `nomis-dirtree-goto-previous-up-from-position-and-display`.
nomis-dirtree: Add doc strings to interactive commands.
nomis-dirtree: Some re-ordering of functions.