You simply install a NuGet package in your IDE to get all and the latest UnityEngine libraies. If you're tired to copy 100+ libraries into your project this is a great solution for you.
Installation is done by using the RocketModFix.UnityEngine.Redist NuGet package.
If you want to update redist then run update.bat and input the path to the Unturned Managed directory, and commit ;)