Allow Filters on different sources to share the same name

Allows Posts and Comments to both use the IsNew filter with their own implementations.

SieveUnitTests/Entities/Comment.cs

@@ -1,9 +1,15 @@
-namespace SieveUnitTests.Entities
+using System;
+using Sieve.Attributes;
+
+namespace SieveUnitTests.Entities
 {
 	public class Comment
     {
         public int Id { get; set; }
 
+        [Sieve(CanFilter = true, CanSort = true)]
+        public DateTimeOffset DateCreated { get; set; } = DateTimeOffset.UtcNow;
+
         public string Text { get; set; }
     }
 }