* 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

Sieve.Sample/Properties/launchSettings.json

@@ -0,0 +1,28 @@
+{
+  "iisSettings": {
+    "windowsAuthentication": false,
+    "anonymousAuthentication": true,
+    "iisExpress": {
+      "applicationUrl": "http://localhost:65136/",
+      "sslPort": 0
+    }
+  },
+  "profiles": {
+    "IIS Express": {
+      "commandName": "IISExpress",
+      "launchBrowser": true,
+      "launchUrl": "api/values",
+      "environmentVariables": {
+        "ASPNETCORE_ENVIRONMENT": "Development"
+      }
+    },
+    "SieveTests": {
+      "commandName": "Project",
+      "launchUrl": "api/values",
+      "environmentVariables": {
+        "ASPNETCORE_ENVIRONMENT": "Development"
+      },
+      "applicationUrl": "http://localhost:6500/"
+    }
+  }
+}