Feature Request - Sorting Keys

I might look into contributing this if I find the time later.

What I am thinking is that it would be something similar to the following python code

``` python
>>> json.dumps({'asdf': 'jkl', '2': 'two'})
'{"asdf": "jkl", "2": "two"}'
>>> json.dumps({'asdf': 'jkl', '2': 'two'}, sort_keys=True)
'{"2": "two", "asdf": "jkl"}'
>>>
```