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.

Start at the fire.Fire(run) entry point shown in the issue and trace how Python modules and their attributes are resolved. Check how hardcoded functions are selected, then determine where module-level __getattr__ or __call__ could be considered as fallbacks. Done means command-line names still invoke hardcoded functions and otherwise use the requested module fallback behavior.

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