Added /json. Valides a json and returns it. It accepts GET and POST requests

```

➜  ~  http POST http://127.0.0.1:5000/json test=test help=why mmmh:='{"key": "value"}' 
HTTP/1.0 200 OK
Content-Length: 73
Content-Type: application/json
Date: Wed, 22 Aug 2012 22:36:30 GMT
Server: Werkzeug/0.8.1 Python/2.7.2

{
    "help": "why", 
    "mmmh": {
        "key": "value"
    }, 
    "test": "test"
}
```