Added support for viewing formatted xml and json

Hi - I spoke to you in person regarding this feature. I've gone ahead and added support for formatting xml and json. However, after our brief discussion I refactored the code so that it only shows the raw ouput for other contents and it's easy to add new content type formatters if need be. Currently I'm using vkbeautify.js (MIT license) to format the response, however this can easily be changed.

Let me know what you think! Thanks

Hattan