Allow arguments for "nimrod run"

With `nimrod run foo 10` I get the error
```
Error: arguments can only be given if the '--run' option is selected
```

Writing `nimrod --run run` is repetitive.

This patch adds `optRun` to the options it in `processCmdLine`, which doesn't seem like the right place to do it. I wanted to add it in `mainCommand`, but the compiler would already stop before reaching that proc.