Use JSON.parse and JSON.stringify instead of goog.json

Hey @r0man, great library!

I'm currently working on a Chrome extension using this and ran into a problem with goog.json.  Apparently Chrome doesn't like it when you run eval(...) in an extension, throwing an error and not allowing you to parse.

This fix does the trick, and removes a dependency!
Here's the browser compatibility for the native JSON fns: http://caniuse.com/json

Cheers,
Conner