Add basic Xamarin.iOS support

csharp/Facebook.Yoga/ios/ApiDefinition.cs

@@ -0,0 +1,13 @@
+using System;
+
+using UIKit;
+using Foundation;
+using ObjCRuntime;
+using CoreGraphics;
+
+namespace Facebook.Yoga.iOS
+{
+	// We're actually abusing the Xamarin.iOS binding project
+	// to bundle in the static lib for us. There is no objective-c
+	// lib to bind, but the build will fail without ApiDefinition.cs
+}