Added explicit support for .NET 4.6.1 and .NET Core 2.0.

Eliminates the need for interfacing libraries reducing the footprint of an application built with the CommandLine library.

Author: ravenpride

src/CommandLine/CommandLine.csproj

@@ -3,7 +3,7 @@
   <PropertyGroup>
     <AssemblyName>CommandLine</AssemblyName>
     <OutputType>Library</OutputType>
-    <TargetFramework>netstandard2.0</TargetFramework>
+    <TargetFrameworks>netstandard2.0; net461; netcoreapp2.0</TargetFrameworks>
     <DefineConstants>$(DefineConstants);CSX_EITHER_INTERNAL;CSX_REM_EITHER_BEYOND_2;CSX_ENUM_INTERNAL;ERRH_INTERNAL;ERRH_DISABLE_INLINE_METHODS;CSX_MAYBE_INTERNAL;CSX_REM_EITHER_FUNC</DefineConstants>
     <DefineConstants Condition="'$(BuildTarget)' != 'fsharp'">$(DefineConstants);SKIP_FSHARP</DefineConstants>
     <GenerateDocumentationFile>true</GenerateDocumentationFile>