Strings args do not need to be parsed.

```
def test(a, b):
print(a, b)

if __name__ == "__main__":
fire.Fire(test)
```

`python .\test.py 1 '2 3'`
```1 2 3```

`python .\test2.py 1 '""2 3""'`
`1 2 3`

`python .\test.py 1 '--2 3'`
```ERROR: The function received no value for the required argument: b```

`python .\test.py 1 '\"2 3\"'`
```
1 "2
ERROR: Could not consume arg: 3"
```

`python .\test.py 1 '\"\"2 3\"\"'`
`1 ""2 3""`

The correct behavior should be equivalent to `print(1, "2 3")`, so strings args do not need to be parsed.