Converted class library into SDK format

Changed to dotnet standard 2.0
Bumped sample and test framework to compatible version

PInvokeSerialPort.Sample/PInvokeSerialPort.Sample.csproj

@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="utf-8"?>
-<Project ToolsVersion="4.0" DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+<Project ToolsVersion="12.0" DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
   <PropertyGroup>
     <Configuration Condition=" '$(Configuration)' == '' ">Debug</Configuration>
     <Platform Condition=" '$(Platform)' == '' ">x86</Platform>
@@ -10,8 +10,9 @@
     <AppDesignerFolder>Properties</AppDesignerFolder>
     <RootNamespace>PInvokeSerialPort.Sample</RootNamespace>
     <AssemblyName>PInvokeSerialPort.Sample</AssemblyName>
-    <TargetFrameworkVersion>v4.0</TargetFrameworkVersion>
-    <TargetFrameworkProfile>Client</TargetFrameworkProfile>
+    <TargetFrameworkVersion>v4.6.1</TargetFrameworkVersion>
+    <TargetFrameworkProfile>
+    </TargetFrameworkProfile>
     <FileAlignment>512</FileAlignment>
   </PropertyGroup>
   <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|x86' ">
@@ -23,6 +24,7 @@
     <DefineConstants>DEBUG;TRACE</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
+    <Prefer32Bit>false</Prefer32Bit>
   </PropertyGroup>
   <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Release|x86' ">
     <PlatformTarget>x86</PlatformTarget>
@@ -32,6 +34,7 @@
     <DefineConstants>TRACE</DefineConstants>
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
+    <Prefer32Bit>false</Prefer32Bit>
   </PropertyGroup>
   <ItemGroup>
     <Reference Include="System" />
@@ -52,6 +55,9 @@
       <Name>PInvokeSerialPort</Name>
     </ProjectReference>
   </ItemGroup>
+  <ItemGroup>
+    <None Include="app.config" />
+  </ItemGroup>
   <Import Project="$(MSBuildToolsPath)\Microsoft.CSharp.targets" />
   <!-- To modify your build process, add your task inside one of the targets below and uncomment it. 
        Other similar extension points exist, see Microsoft.Common.targets.

PInvokeSerialPort.Sample/app.config

@@ -0,0 +1,3 @@
+<?xml version="1.0" encoding="utf-8"?>
+<configuration>
+<startup><supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.6.1"/></startup></configuration>