Modified to add AMD registration

Register Backbone.LocalStorage as a AMD module.

Example of usage:
```javascript

  // Example configuration for require.js
  require.config({
    baseUrl:'js',
    paths: {
      jquery : 'https://ajax.googleapis.com/ajax/libs/jquery/1/jquery.min',      
      backbone : 'lib/backbone',
      underscore: 'lib/underscore',
      localstorage: 'lib/backbone.localStorage'
    },
    shim: {
      'backbone': {
        //These script dependencies should be loaded before loading
        //backbone.js
        deps: ['lib/underscore', 'jquery'],
        //Once loaded, use the global 'Backbone' as the
        //module value.
        exports: 'Backbone'
      },
      'localstorage': {
        //These script dependencies should be loaded before loading
        //backbone.localstorage.js
        deps: ['backbone'],
        //Once loaded, use the global 'Backbone.LocalStorage' as the
        //module value.
        exports: 'Backbone.LocalStorage'
      }
    }
  });

  define('someCollection', ['backbone', 'localstorage'], function(Backbone, LocalStorage) {
    return Backbone.Collection.extend({
      localStorage: new LocalStorage('SomeCollection') // Unique name within your app.
    });
  });

  require(['someCollection'], function(someCollection) {
    // use someCollection
  });

```
Build status: https://travis-ci.org/nekman/Backbone.localStorage