Create new field for multi line text inputs

I've created a reliable way of adding lists of textboxes.
In the field options, specifying the rows will create that many lines.
Then the options array is defined as Label => field and as many fields per line you need.

e.g.

```php
$meta_boxes[] = array(
    'id'    => 'top10_metabox',
    'title' => 'Favourite Tunes',
    'pages' => 'some pages',

    'fields' => array(
      array(
        'name' => 'Top Tracks',
        'id'   => $prefix . 'toptrack',
        'desc' => 'Your Top Tunes go here.',
        'type' => 'fieldset_text',
        'rows' => 10,
        
        'options' => array(
          'Artist' => 'artist',
          'Track'  => 'track',
          'Link'   => 'link',
        ),
      ),
    ),
  );
```