code: public void addOption(String key, char shortKey,
        Command<? super T> handler) {
      options.put(key, handler);
      shortcuts.put(shortKey, key);
    }
docs: Add a command line option handler.
  @param key The <code>String</code> that identifies this option.  The
  option may be triggered by specifying <code>--&lt;key&gt;</code>
  on the command line.
  @param shortKey The <code>char</code> that serves as a shortcut to the
  option.  The option may be triggered by specifying
  <code>-&lt;shortKey&gt;</code> on the command line.
  @param handler The <code>Command</code> that is used to process the
  option.