Add the PluginTest project.
Change the PluginTest target framework to 3.5.

Remove 4.x assembly references.
Ignore the Unity3D.DLLs NuGet package.
Add a sentinel file and remove it during package installation.

Use the technique described for the FluentMigrator.Tools NuGet package
to add a sentinel file to the content/ directory, and remove it during
installation. This forces NuGet to install the package per-project, even
though it's technically a tools-only package.
Install the Unity3D.DLLs package in the PluginTest project.

This will also set up NuGet package restore in the project.
Add packages.config to the PluginTest project.
Add a bare-bones PowerShell module for Unity3D.DLLs.

Install the module from init.ps1.
Add the content directory to the solution.
Add a PS function to get the path to the installed Unity Editor.
Don't export variables from the PS module.
Add detection of Unity 3D managed DLLs.

Begin the flow of updating project assembly references using what's
found in the Unity Editor's managed DLL directory.
Add a full reference to UnityEngine.dll to PluginTest, for testing.