Added project rubberband-dll to create Windows DLL files (32-bit and 64-bit)

that expose the Rubber Band API as a flat API that can be imported through
runtime linking.

Added project rubberband-sharp to provide a .NET wrapper of the rubberband-dll
files, dynamically dispatching to the 32- or 64-bit DLL based on the process
platform. Configured NuGet package creation, with compatibility for both
packages.config and PackageReference style consumers.

rubberband-dll/stdafx.h

@@ -0,0 +1,16 @@
+// stdafx.h : include file for standard system include files,
+// or project specific include files that are used frequently, but
+// are changed infrequently
+//
+
+#pragma once
+
+#include "targetver.h"
+
+#define WIN32_LEAN_AND_MEAN             // Exclude rarely-used stuff from Windows headers
+// Windows Header Files
+#include <windows.h>
+
+#include <RubberBandStretcher.h>
+
+// reference additional headers your program requires here