[dotnet] Add dotnet projects and examples

+ Sitemap generator I created while learning the dispose pattern
+ Testing project for learning general C#

dotnet/testing/README.md

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+This is a testing project I created while first learning C#.
+There's no objective or goal, aside from playing with different features of C# and NuGet packages.
+Essentially, this is a scrap project that I code in while learning new C# things.
+Since this is just for learning, I won't bother explaining how to use things here; It's very possible this entire project could disappear one day.