Update README with API updates

Author: ericleich

unity/README.md

@@ -8,13 +8,12 @@ applications. Plugin features include:
 * A single package with cross platform (Android/iOS) support
 * Mock ad calls when running inside Unity editor
 * Support for Banner Ads
+* Support for Interstitial Ads
 * Custom banner sizes
 * Banner ad events listeners
 * AdRequest targeting methods
 * A sample project to demonstrate plugin integration
 
-Interstitial support coming soon.
-
 The plugin contains a .unitypackage file for those that want to easily import
 the plugin, as well as the source code for those that want to iterate on it.
 
@@ -109,6 +108,27 @@ Here is the minimal code needed to create a banner.
 
 The _AdPosition_ enum specifies where to place the banner.
 
+Basic Interstitial Flow
+-----------------------
+Here is the minimal banner code to create an interstitial.
+
+    using GoogleMobileAds.Api;
+    ...
+    // Initialize an InterstitialAd.
+    InterstitialAd interstitial = new InterstitialAd("MY_AD_UNIT_ID");
+    // Create an empty ad request.
+    AdRequest request = new AdRequest.Builder().Build();
+    // Load the interstitial with the request.
+    interstitial.LoadAd(request);
+
+Unlike banners, interstitials need to be explicitly shown. At an appropriate
+stopping point in your app, check that the interstitail is ready before
+showing it:
+
+    if (interstitial.isLoaded()) {
+      interstitial.Show();
+    }
+
 Custom Ad Sizes
 ---------------
 In addition to constants on _AdSize_, you can also create a custom size:
@@ -161,7 +181,10 @@ also want to get test ads on the simulator. Here is how to set up the request:
 
 Ad Events
 ---------
-_BannerView_ contains ad events that you can register for:
+Both _BannerView_ and _InterstitialAd_ contain the same ad events that you can
+register for. These events are of type
+[EventHandler](http://msdn.microsoft.com/en-us/library/db0etb8x%28v=vs.110%29.aspx).
+Here we'll demonstrate setting ad events on a banner:
 
     using GoogleMobileAds.Api;
     ...
@@ -182,12 +205,21 @@ _BannerView_ contains ad events that you can register for:
     bannerView.AdLeftApplication += HandleAdLeftApplication;
     ...
 
-    public void HandleAdLoaded()
+    public void HandleAdLoaded(object sender, EventArgs args)
     {
         print("HandleAdLoaded event received.");
         // Handle the ad loaded event.
     }
 
+The only event with special event args is _AdFailedToLoad_. It passes an
+instance of _AdFailedToLoadEventArgs_ with a _Message_ describing the error.
+
+    public void HandleAdFailedToLoad(object sender, AdFailedToLoadEventArgs args)
+    {
+      print("Interstitial Failed to load: " + args.Message);
+      // Handle the ad failed to load event.
+    };
+
 You only need to register for the events you care about.
 
 Banner Lifecycle
@@ -208,6 +240,15 @@ your reference to it:
 This lets the plugin know you no longer need the object, and can do any
 necessary cleanup on your behalf.
 
+Interstitial Lifecycle
+----------------------
+Similar to banners, interstitials also have a destroy method:
+
+    interstitial.Destroy();
+
+It is important to explicitly destroy the interstitial before letting it go
+out of scope so that it can be properly released by the plugin.
+
 Additional Resources
 ====================
 * [Developer documentation](https://developers.google.com/mobile-ads-sdk/docs)