Give user more control over fetch time

Currently, $script uses a setTimeout() call to defer script fetching which makes it difficult to execute javascript before the DOMContentLoaded event fires. Removing the setTimeout() will make it more transparent to the user when $script fetches the script and when the callback gets executed:

```html
<!-- in <head> -->
<script>
  // load jquery.js before DOMContentLoaded
  $script('path-to-jquery.js', 'jquery');

  // load jquery-plugin.js after DOMContentLoaded   
  $script.ready('jquery', function() {
    jQuery(document).ready(function() {
      $script('path-to-jquery-plugin.js');
    });
  });
</script>
```