title: Swift 2/3 String implement of rindexOf method
body: <p>I know there is an build in method to get the index of substring from the original string by using <code>rangeOfString</code>. But it is used to get the <strong>first occurrence</strong> of a given substring. However what I need to do is to get the <strong>last occurrence</strong> of the given substring.</p>
  
  <p>This is something like the <code>rindex</code> in python language</p>
  
  <p>So, my question is, How can I do that in Swift 2.x/3? A code snippet example is appreciated.</p>