Add an extra token for formatted json

I had been doing this stuff outside of debug and just passing in a string for the json rather than an object. This isn't great though since you end up paying the cost of serializing the JSON even if it isn't going to be logged.  

![Screenshot from 2013-01-14 13:54:57](https://f.cloud.github.com/assets/1103796/63501/8bbe0570-5de5-11e2-84b5-2b46fc14c196.png)

I haven't done anything with the browser version but I think since the browser won't understand `%pj` everything should be fine so long as the data is the last argument. Which in all my use cases so far it is.