Add basic Xamarin.Mac support

Summary:
- Does not contain "magic" found in YogaKit yet, but enough to get started
- Simple test project showing use
- YGInteropSetLogger and YGNodeInit(IntPtr) were missing from native lib built by buck
Closes https://github.com/facebook/yoga/pull/278

Reviewed By: emilsjolander

Differential Revision: D4388480

Pulled By: splhack

fbshipit-source-id: a7387bb5b5554b6fce80d08c23e4fa18a4611cce

csharp/Mac/Facebook.Yoga.Mac.Test/ViewController.designer.cs

@@ -0,0 +1,18 @@
+// WARNING
+//
+// This file has been generated automatically by Xamarin Studio to store outlets and
+// actions made in the UI designer. If it is removed, they will be lost.
+// Manual changes to this file may not be handled correctly.
+//
+using Foundation;
+
+namespace Facebook.Yoga.Mac.Test
+{
+	[Register("ViewController")]
+	partial class ViewController
+	{
+		void ReleaseDesignerOutlets()
+		{
+		}
+	}
+}