Helper to handle saving/fetching JSON to URL hash.

Useful for presisting user settings in the URL's hash fragment.
When the user refreshes the page, you can fetch those settings directly from the URL.

Example:
Hash.set({my_id:1, your_id:2, your_name:"John"}); // http://www.example.com#{my_id:1,your_id:2,your_name:John}
Hash.get('my_id'); // Returns 1

Notice that the JSON in the URL has no double quotes. This is because they
get stripped when transmitted in emails. If you put spaces in a string, they
will gracefully be escaped in the URL.

Author: Martin Drapeau
Copyright 2009-2012 Planbox Inc.
Note: Requires json2.js (https://github.com/douglascrockford/JSON-js)