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/Services/SieveCustomFilterMethods.cs

@@ -1,4 +1,5 @@
-using System.Linq;
+using System;
+using System.Linq;
 using Sieve.Services;
 using SieveUnitTests.Entities;
 
@@ -13,6 +14,13 @@ namespace SieveUnitTests.Services
             return result;
         }
 
+        public IQueryable<Comment> IsNew(IQueryable<Comment> source, string op, string value)
+        {
+            var result = source.Where(c => c.DateCreated > DateTimeOffset.UtcNow.AddDays(-2));
+
+            return result;
+        }
+
         public IQueryable<Comment> TestComment(IQueryable<Comment> source, string op, string value)
         {
             return source;