Refactoring c# projects (#544)

Small Refactoring c# projects, e.g.
* add days
* remove StartupObject
* Fix Approval tests for NUnit
* Use Environment.NewLine in Xunit tests
* Added + fixed README.md
* Removed global.json

csharp.xUnit/GildedRose/Item.cs

@@ -1,9 +1,8 @@
-namespace GildedRoseKata
+namespace GildedRoseKata;
+
+public class Item
 {
-    public class Item
-    {
-        public string Name { get; set; }
-        public int SellIn { get; set; }
-        public int Quality { get; set; }
-    }
-}
+    public string Name { get; set; }
+    public int SellIn { get; set; }
+    public int Quality { get; set; }
+}