Fix package error and .gitignore (#31)

Author: peiche-ms

.gitignore

@@ -1,3 +1,7 @@
 # VS Code
 .vs/
 .vscode/
+packages/
+
+*.csproj.user
+*.vcxproj.user

WebView2APISample/WebView2APISample.vcxproj

@@ -250,14 +250,14 @@
   </ItemGroup>
   <Import Project="$(VCTargetsPath)\Microsoft.Cpp.targets" />
   <ImportGroup Label="ExtensionTargets">
-    <Import Project="packages\Microsoft.Windows.ImplementationLibrary.1.0.191107.2\build\native\Microsoft.Windows.ImplementationLibrary.targets" Condition="Exists('packages\Microsoft.Windows.ImplementationLibrary.1.0.191107.2\build\native\Microsoft.Windows.ImplementationLibrary.targets')" />
-    <Import Project="packages\Microsoft.Web.WebView2.0.9.488-prerelease\build\native\Microsoft.Web.WebView2.targets" Condition="Exists('packages\Microsoft.Web.WebView2.0.9.488-prerelease\build\native\Microsoft.Web.WebView2.targets')" />
+    <Import Project="..\packages\Microsoft.Windows.ImplementationLibrary.1.0.191107.2\build\native\Microsoft.Windows.ImplementationLibrary.targets" Condition="Exists('..\packages\Microsoft.Windows.ImplementationLibrary.1.0.191107.2\build\native\Microsoft.Windows.ImplementationLibrary.targets')" />
+    <Import Project="..\packages\Microsoft.Web.WebView2.0.9.488-prerelease\build\native\Microsoft.Web.WebView2.targets" Condition="Exists('..\packages\Microsoft.Web.WebView2.0.9.488-prerelease\build\native\Microsoft.Web.WebView2.targets')" />
   </ImportGroup>
   <Target Name="EnsureNuGetPackageBuildImports" BeforeTargets="PrepareForBuild">
     <PropertyGroup>
       <ErrorText>This project references NuGet package(s) that are missing on this computer. Use NuGet Package Restore to download them.  For more information, see http://go.microsoft.com/fwlink/?LinkID=322105. The missing file is {0}.</ErrorText>
     </PropertyGroup>
-    <Error Condition="!Exists('packages\Microsoft.Windows.ImplementationLibrary.1.0.191107.2\build\native\Microsoft.Windows.ImplementationLibrary.targets')" Text="$([System.String]::Format('$(ErrorText)', 'packages\Microsoft.Windows.ImplementationLibrary.1.0.191107.2\build\native\Microsoft.Windows.ImplementationLibrary.targets'))" />
-    <Error Condition="!Exists('packages\Microsoft.Web.WebView2.0.9.488-prerelease\build\native\Microsoft.Web.WebView2.targets')" Text="$([System.String]::Format('$(ErrorText)', 'packages\Microsoft.Web.WebView2.0.9.488-prerelease\build\native\Microsoft.Web.WebView2.targets'))" />
+    <Error Condition="!Exists('..\packages\Microsoft.Windows.ImplementationLibrary.1.0.191107.2\build\native\Microsoft.Windows.ImplementationLibrary.targets')" Text="$([System.String]::Format('$(ErrorText)', '..\packages\Microsoft.Windows.ImplementationLibrary.1.0.191107.2\build\native\Microsoft.Windows.ImplementationLibrary.targets'))" />
+    <Error Condition="!Exists('..\packages\Microsoft.Web.WebView2.0.9.488-prerelease\build\native\Microsoft.Web.WebView2.targets')" Text="$([System.String]::Format('$(ErrorText)', '..\packages\Microsoft.Web.WebView2.0.9.488-prerelease\build\native\Microsoft.Web.WebView2.targets'))" />
   </Target>
 </Project>