Parse short options in order given

Fixes:
* Short options cannot be repeated in the same group:
  e.g., `-nn` fails, but `--null-input --null-input` works
* Short options are processed in an arbitrary fixed order, not the order
  given by the user: e.g., `-hV`, `-Vh`, `-h -V`, and `--help --version`
  are processed as `-h`, but `-V -h` and `--version --help` are
  processed as `-V`
* `-L` cannot be a part of a short option group (as the last one):
  e.g., `-nLlib` and `-nL lib` fail

Author: thaliaarchi