title: Issue with encoding "&" in URLs
body: <p>I've got to send a https GET request to a web service in my iPhone app which is developing in Swift 1.2.</p>
  
  <p>I am trying to construct query string parameters but got to encode them before send to server.</p>
  
  <p>All good but not working when password contains '&amp;' charcter. Expect to encode '&amp;' character to '%26' but NOT working...</p>
  
  <p>Just done a test when having '%'. Works as expected with '%' providing '%25'. But NOT convert '&amp;' sign....</p>
  
  <p>Tried following ways:</p>
  
  <pre><code>var testPassword1: String = "mypassword&amp;1"
  
  var testPassword2: String = "mypassword%1"
  
  
  // Try to encode 'testPassword1'
  testPassword1.stringByAddingPercentEscapesUsingEncoding(NSUTF8StringEncoding)! 
  testPassword1.stringByAddingPercentEncodingWithAllowedCharacters(.URLHostAllowedCharacterSet())!
  
  
  // Try to encode 'testPassword2'
  testPassword2.stringByAddingPercentEscapesUsingEncoding(NSUTF8StringEncoding)!
  testPassword2.stringByAddingPercentEncodingWithAllowedCharacters(.URLHostAllowedCharacterSet())!
  </code></pre>
  
  <p>I've done the above tests and following are the response</p>
  
  <p><a href="https://i.stack.imgur.com/w0iG4.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/w0iG4.png" alt="enter image description here"></a></p>
  
  <p>Would like to know the correct way to do this. Thanks.</p>