* 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/Services/ApplicationSieveProcessor.cs

@@ -0,0 +1,24 @@
+using Microsoft.Extensions.Options;
+using Sieve.Models;
+using Sieve.Sample.Entities;
+using Sieve.Services;
+
+namespace Sieve.Sample.Services
+{
+    public class ApplicationSieveProcessor : SieveProcessor
+    {
+        public ApplicationSieveProcessor(IOptions<SieveOptions> options, ISieveCustomSortMethods customSortMethods, ISieveCustomFilterMethods customFilterMethods) : base(options, customSortMethods, customFilterMethods)
+        {
+        }
+
+        protected override SievePropertyMapper MapProperties(SievePropertyMapper mapper)
+        {
+            mapper.Property<Post>(p => p.Title)
+                .CanSort()
+                .CanFilter()
+                .HasName("CustomTitleName");
+
+            return mapper;
+        }
+    }
+}