Adding AsyncObservable and AsyncObserver classes.

AsyncRx.NET/System.Reactive.Async/System.Reactive.Async.csproj

@@ -4,8 +4,4 @@
     <TargetFramework>netstandard2.0</TargetFramework>
   </PropertyGroup>
 
-  <ItemGroup>
-    <Folder Include="System\Reactive\Linq\" />
-  </ItemGroup>
-
 </Project>

AsyncRx.NET/System.Reactive.Async/System/Reactive/Linq/AsyncObservable.cs

@@ -0,0 +1,10 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the Apache 2.0 License.
+// See the LICENSE file in the project root for more information. 
+
+namespace System.Reactive.Linq
+{
+    public static class AsyncObservable
+    {
+    }
+}

AsyncRx.NET/System.Reactive.Async/System/Reactive/Linq/AsyncObserver.cs

@@ -0,0 +1,10 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the Apache 2.0 License.
+// See the LICENSE file in the project root for more information. 
+
+namespace System.Reactive.Linq
+{
+    public static class AsyncObserver
+    {
+    }
+}