title: How to only allow alphanumeric using ng-pattern-restrict for first character only?
body: <p>I'm using <a href="https://github.com/AlphaGit/ng-pattern-restrict" rel="noreferrer">https://github.com/AlphaGit/ng-pattern-restrict</a> to restrict input.  What I"m trying to do is only allow alphanumeric for the first character ONLY.  The problem is if I use : </p>
  
  <p><code>ng-pattern-restrict="^[a-zA-Z0-9]+"</code> </p>
  
  <p>it works, but won't allow user to clear the whole string, which I would also like as an option.</p>