Feature: `ls -l` style listing format

- Add `ls -l` style listing (with `-l -v`). Not as perfect as ls, but...

- Add `--sz-human-readable` to print file size in a readable format with
  `ls -l` style.

- Make it possible to increase verbosity by specifying `-v` for multiple
  times. Not in use, though.

- Dump error string in `path_create_ancestors()`.

- Correct some issues in documentation. Code clean-up.