Support __call__ and __getattr__ on module

Given code like this:

```python
def hardcoded():
# ...

def __getattr__(name):
# ...

def __call__(*args):
# ...

if __name__ == '__main__':
fire.Fire(run)
```

I would like fire to call `hardcoded` function when `hardcoded` is specified on command line. Otherwise, I would like it to fall back on `__getattr__` or `__call__`. I don't care which one, but I think both can be supported at the same time with `__getattr__` being tried first.

Current workaround is to use helper object with `__call__` method on it, but that hides all global functions in the module, so forwarding methods have to be added to the helper object.