title: How to implement GMUClusterRenderer in Swift
body: <p>I am using Google Maps API for iOS and want to use marker clustering utility. I figured out how to show clustered markers, but I would like to customize markers. Can someone explain how to set/change icon and title of each marker or clustered markers? An example code would be very helpful.</p>
  
  <pre><code>class POIItem: NSObject, GMUClusterItem {
      var position: CLLocationCoordinate2D
      var name: String!
  
      init(position: CLLocationCoordinate2D, name: String) {
          self.position = position
          self.name = name
      }
  }
  
  class MyRenderer: NSObject, GMUClusterRenderer {
      var mapView: GMSMapView
      var clusterIconGenerator: GMUClusterIconGenerator
      var clusterManager: GMUClusterManager
  
      init(mapView: GMSMapView, clusterIconGenerator: GMUClusterIconGenerator, clusterManager: GMUClusterManager) {
          self.mapView = mapView
          self.clusterIconGenerator = clusterIconGenerator
          self.clusterManager = clusterManager
      }
  
      func renderClusters(clusters: [GMUCluster]) {
  
      }
  
      func update() {
  
      }
  }
  </code></pre>
  
  <p>This is what I have so far. I don't know what to do with renderClusters and update functions.</p>