title: Calculate range count in Swift 3
body: <p>Apparently before Swift 3, a <code>Range&lt;String.Index&gt;</code> had a <code>count</code> property. While migrating to Swift 3 I noticed that this <code>count</code> property is now gone. How do I calculate the distance between 2 <code>String.Index</code>es in Swift 3?</p>