Options::parse() should complain about unsupported options and should print help

This code:
```
int
main(int argc, char* argv[]) {
  Options opt("Testcase");
  opt.iterations(200);
  opt.parse(argc,argv);
  Script::run<Testcase,DFS,Options>(opt);
  return 0;
}
```
doesn't complain about bad arguments and doesn't print help.

It would be great if it would become a bit more user friendly.
