Added Sync object for SDL

Source/OpenTK/OpenTK.csproj

@@ -798,6 +798,7 @@
     <Compile Include="Platform\SDL2\Sdl2NativeWindow.cs" />
     <Compile Include="Platform\SDL2\Sdl2WindowInfo.cs" />
     <Compile Include="Platform\MacOS\Cgl.cs" />
+    <Compile Include="Platform\SDL2\Sdl2.cs" />
   </ItemGroup>
   <Import Project="$(MSBuildBinPath)\Microsoft.CSharp.targets" />
   <PropertyGroup>

Source/OpenTK/Platform/SDL2/Sdl2.cs

@@ -1,3 +1,30 @@
+#region License
+//
+// The Open Toolkit Library License
+//
+// Copyright (c) 2006 - 2013 Stefanos Apostolopoulos for the Open Toolkit library.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights to 
+// use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
+// the Software, and to permit persons to whom the Software is furnished to do
+// so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in all
+// copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
+// OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
+// HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
+// WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+// OTHER DEALINGS IN THE SOFTWARE.
+//
+#endregion
+
 using System;
 
 namespace OpenTK.Platform.SDL2