title: Clear UIPasteBoard
body: <p>Lets assume that 3 strings have been copied on the UIPasteBoard:</p>
  
  <pre><code>UIPasteboard.generalPasteboard().string="hello"
  UIPasteboard.generalPasteboard().string="world"
  UIPasteboard.generalPasteboard().string="!"
  </code></pre>
  
  <p>I use 
      UIPasteboard.generalPasteboard().string=""</p>
  
  <p>Will it clear the pasteboard? Is there any similar func for UIPasteBoard like there is clearContents()  for NSPasteBoard?</p>