* Migrate tests to xunit

* Update sample project to dotnetcore3.1
* Use Sqlite in sample project to run it everywhere
* Fix: Filter with escaped comma
* Fix: Filter "null" does not work with Contains or StartsWith
* Code cleanup: Adjust namespaces, adjust usings

SieveUnitTests/Entities/Comment.cs

@@ -7,5 +7,8 @@ namespace SieveUnitTests.Entities
     {
         [Sieve(CanFilter = true)]
         public string Text { get; set; }
+        
+        [Sieve(CanFilter = true)]
+        public string Author { get; set; }
     }
 }