Cleanup & Fixes for .NET 5 (#309)

- [X] Fixes several bugs
- [X] Updates more ordinal issues
- [X] Cleans up the code a bit
- [X] Turns classes static that should have been
- [X] Changes TcpServer.Instances to a HashSet

Bumps release version

Projects/Server/Insensitive.cs

@@ -19,6 +19,6 @@ namespace Server
             a != null && b != null && a.Length >= b.Length && Comparer.Compare(a.Substring(a.Length - b.Length), b) == 0;
 
         public static bool Contains(string a, string b) =>
-            a != null && b != null && a.Length >= b.Length && a.IndexOf(b, StringComparison.OrdinalIgnoreCase) >= 0;
+            a != null && b != null && a.Length >= b.Length && a.Contains(b, StringComparison.Ordinal);
     }
 }