Add data-content='item' attribute to the generated span tags.

Add <tt>data-content='item'</tt> attribute to the generated span tags. 

This hook allows for dynamic use of :before and :after pseudo elements to layer text by way of a attr() call.

```` css
span.char1:before {
  content: attr(data-content);
  ... 
}
````

No more hard coding textual content in css files!