new feature: auto-update of locale-dependant names when locale changes

Since the locale can be changed in a single-page app, it can be a good idea to update the parser when it does.

The service has been modified to define a provider.

If you wish that the service should be automatically updated when the locale changes, you may instruct it to do so using the provider:

```javascript
angular.module('myApp', ['dateParser'])
  .config(function($dateParserProvider) {
	$dateParserProvider.watchLocale(true);
  })
```

You also may update it manually:

```javascript
$dateParser.updateFromLocale();
```