Allows noResultsText to be set to a function.

Includes an example in demo.html.

This is particularly useful in combination with the `allowFreeTagging` option. The function receives two arguments, a HTML-escaped query string and the results array (which should always be empty).

When defined as a string the normal behaviour occurs, the string is wrapped in a paragraph element and injected into the DOM.

When defined as a function, the returned value is injected into the DOM.

So instead of _"No tag found..."_ you could have it update in real time _"Creating a new tag: Targaryen..."_.