Allow disordered options for obgen

In the man page of ```obgen``` tool, it is described that it should be called as bellow.
```obgen [OPTIONS] filename```

On the other hand, ```obgen``` says it should be called as bellow and it actually should be.
```obgen <filename> [options]```

I've wrote the patch that makes ```obgen``` accept both forms.
Please take a look at it.