DateOnly Extension demonstration

[Mike-E-angelo]

Addresses #608

[AppVeyorBot]

:white_check_mark: Build ExtendedXmlSerializer 3.7.11.3-ykwguwtq completed (commit https://github.com/ExtendedXmlSerializer/home/commit/63b0e13f75 by @Mike-E-angelo)

Install it by running the following command in Package Manager Console:

Install-Package ExtendedXmlSerializer -Version 3.7.11.3-ykwguwtq -Source https://ci.appveyor.com/nuget/extendedxmlserializer-preview

Problems with the above command? You may be running into this known issue here: https://github.com/NuGet/Home/issues/7189