Update C# wrapper to support both desktop and UWP projects

Summary:
The C# wrapper project has been changed to a NETStandard (1.1) PCL allowing it
to be consumed by any project targeting .NET4.5 or greater including .NETCore
and UWP projects... The C# wrapper uses P/Invoke to call into the Native Yoga
DLL...

The "Yoga" C++ project has been updated to support ARM builds...

Added the ability to generate nuget packages for the C# wrapper that supports
copying the native DLLs to the target output directory.

Closes: https://github.com/facebook/yoga/pull/283

Reviewed By: splhack, emilsjolander

Differential Revision: D4381455

Pulled By: JoelMarcey

fbshipit-source-id: e6dc4190caa824ac63d5d5ee2eb4c7914efbb00f

csharp/nuget/Facebook.Yoga.Native.nuspec

@@ -0,0 +1,38 @@
+<?xml version="1.0" encoding="utf-8"?>
+<package xmlns="http://schemas.microsoft.com/packaging/2012/06/nuspec.xsd">
+  <metadata>
+    <id>Facebook.Yoga.Native</id>
+    <version>1.0.1-pre</version>
+    <title>Facebook.Yoga.Native</title>
+    <authors>Facebook</authors>
+    <owners>Facebook</owners>
+    <licenseUrl>https://github.com/facebook/css-layout/blob/master/LICENSE</licenseUrl>
+    <projectUrl>https://github.com/facebook/css-layout</projectUrl>    
+    <requireLicenseAcceptance>false</requireLicenseAcceptance>
+    <description>A subset of CSS's flexbox layout algorithm and box model.</description>
+    <copyright>Copyright 2016 Facebook</copyright>
+    <tags>native flexbox flex-box css layout css-layout yoga facebook</tags>
+    <dependencies>
+      <group targetFramework=".NETStandard1.0" />
+    </dependencies>
+  </metadata>
+
+  <files>
+    <!-- build -->
+    <file src="Facebook.Yoga.Native.targets" target="build\netstandard1.0"/>
+
+    <!-- lib -->
+    <file src="_._" target="lib\netstandard1.0"/>
+
+    <!-- Native -->
+    <file src="..\Yoga\bin\x86\Release\Yoga.dll" target="runtimes\win-x86\native"/>
+    <file src="..\Yoga\bin\x86\Release\Yoga.pdb" target="runtimes\win-x86\native"/>
+    
+    <file src="..\Yoga\bin\x64\Release\Yoga.dll" target="runtimes\win-x64\native"/>
+    <file src="..\Yoga\bin\x64\Release\Yoga.pdb" target="runtimes\win-x64\native"/>
+
+    <file src="..\Yoga\bin\ARM\Release\Yoga.dll" target="runtimes\win8-arm\native"/>
+    <file src="..\Yoga\bin\ARM\Release\Yoga.pdb" target="runtimes\win8-arm\native"/>    
+  </files>
+  
+</package>