Some improvements

Hello,
I'm using this library and I made some changes to library for my needs.
In this PR you will find these changes:
1. Added support for multiple locale loading. I needs to load all/some locales and switch between at runtime.
2. Added support to switch between locale at runtime (globally or on instance). Eg.
```js
// require('globalization/en-US');
// require('globalization/it-IT');
Date.setLocale('en-US'); // Set global date locale to en-US

var d1 = new Date(2013, 0, 1);
var d2 = new Date(2013, 0, 1);
console.debug(d1.toString('m')); // => "January 01"
console.debug(d2.toString('m')); // => "January 01"

d2.setLocale('it-IT');
console.debug(d1.toString('m')); // => "January 01"
console.debug(d2.toString('m')); // => "01 gennaio"

```
3. Updated nodeunit to latest version which run on nodejs v0.10.3

I hope my work could be useful.