Improvements, including documentation, are welcome.
Initial focus is on making await foreach and async using working.
In your .NET 4.5.2 or .NET 4.6 (4.6.1, 4.6.2, 4.7, 4.7.1, 4.7.2 have not yet been tested), add a reference to the nuget package TerWoord.CSharp8Support. Then set the C# language level support to 8.0. If you don't have the .NET core 3 sdk installed, you will also need to install the current preview of the Microsoft.Net.Compilers package, so make sure you have the preview compiler.