arg parsing truncates at hash

Fire's arg parser truncates strings with hashes (#) in them. Simple test:

test.py:
```
import fire
def test(a): print(a, type(a))
fire.Fire(test)
```

```
> python test.py hi#there
hi
> python test.py "hi#there"
hi
```

If this is by design, it doesn't appear to be documented anywhere.