Add isEmpty, keys methods. Added Jasmine tests for new and old methods.

Hello,

I found your library very helpful but needed to make a few modifications for easier use.   
1) Added isEmpty method returns true if the storage is empty.
2) Added keys to returns the keys currently in the storage.
3) Added Jasmine tests for existing and new methods.
4) Added boolean to deleteAll. If you pass in true now it will now delete all the variables in storage even if they are outside of the namespace.
5) Reimplemented cookie_storage so it works more like the build in window.localStorage object. This allows all the methods to work correctly with the cookie storage now, such as deleteAll. You can also now use a for loop and Object.keys() with cookie_storage and it will function correctly.
6) Removed the get, set, delete documentation examples for passing in multiple variable arguments outside of an array. For example, get("item1", "item2", "item3"). I was not able to get this syntax working even before I started making modifications. The multiple argument in an array syntax works correctly, however. 

I hope you find these changes helpful. Let me know if you have any questions.

Thanks.
Josh