Refactor

- Display a message when the refactoring is called with no :use form in the ns
  declaration
- No need for this function to be recursive
- The second optional argument to re-search-forward is NOERROR, making
  it possible to remove (ignore-errors ...) wrappers.
- Remove dependence on cl-flet in favor of private function at
  top-level.
- Don't re-implement nreverse. *blush*
- Refactor to use let* instead of let + setq.