csharp-async-console-apps.md

• https://devblogs.microsoft.com/dotnet/welcome-to-c-7-1/#gist82557368
• https://stackoverflow.com/questions/9208921/cant-specify-the-async-modifier-on-the-main-method-of-a-console-app
• https://devblogs.microsoft.com/pfxteam/should-i-expose-synchronous-wrappers-for-asynchronous-methods/