Ability to extend WebFontConfig

If you want for example to add an event to run when fonts finish loading you could use something like: 

```
   function my_webfontConfig() {
       echo "<script type='text/javascript'>";
       echo "if (typeof WebFontConfig === 'undefined') { WebFontConfig = new Object(); }"; 
       echo "WebFontConfig['active'] = function() { alert('Fonts Loaded!') };";
       echo "</script>";
   }
   add_action( 'wp_head', 'my_webfontConfig', 100 );
```