C#8+ addition

[chessboards]

Many features such as default implementations, switch expressions, and others are only available in C#8+, which can lead to confusion since those versions are only available with Visual Studio preview editions. A process on downloading this version would be a helpful addition for until the versions are released outside of preview.

[andrewstellman]

This is definitely an issue we constantly have to contend with, especially with C# 10 and Visual Studio 2022 out now. The current version of the book works with VS2019 and the older version of C#, but when we update it for VS2022 and C# 10 we're planning on covering some of the new features. We'll give some thought to how to handle this so we don't leave out any readers.