Add xml and json responses to the checks for more than just text processing.

This lets us do things like this:

````
GET /up.json
````

````json
{
    "redis": {
        "success": true,
        "message": "Up",
        "timing": "0.810"
    },
    "database": {
        "success": true,
        "message": "Up",
        "timing": "0.431"
    },
    "memcached": {
        "success": true,
        "message": "Up",
        "timing": "0.550"
    },
    "http": {
        "success": false,
        "message": "Down",
        "timing": "0.846"
    }
}
````