title: Objective-C and Swift URL encoding
body: <p>I have a <code>NSString</code> like this:</p>
  
  <pre><code>http://www.
  </code></pre>
  
  <p>but I want to transform it to:</p>
  
  <pre><code>http%3A%2F%2Fwww.
  </code></pre>
  
  <p>How can I do this?</p>