title: Convert string into slug with single-hyphen delimiters only
body: <p>I would  like to sanitize a string in to a URL so this is what I basically need:</p>
  <ol>
  <li>Everything must be removed except alphanumeric characters and spaces and dashed.</li>
  <li>Spaces should be converter into dashes.</li>
  </ol>
  <p>Eg.</p>
  <pre><code>This, is the URL!
  </code></pre>
  <p>must return</p>
  <pre><code>this-is-the-url
  </code></pre>