[dotnet] Add dotnet projects and examples

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

dotnet/sitemap/ConsoleApp/TestFiles/robots.txt

@@ -0,0 +1,9 @@
+User-agent: *
+Disallow:
+Disallow: /dist/
+Disallow: /settings/
+Disallow: /register/
+Disallow: /login/
+Disallow: /uploads/
+Disallow: /export/
+Disallow: /search?