Add support for ObjectId type for the Id of the document.

IntegrationTests/CRUDObjectIdTests.cs

@@ -0,0 +1,19 @@
+using IntegrationTests.Infrastructure;
+using MongoDB.Bson;
+using NUnit.Framework;
+
+namespace IntegrationTests
+{
+    public class ObjectIdTestDocument : TestDoc<ObjectId>
+    {
+    }
+
+    [TestFixture]
+    public class CRUDObjectIdTests : MongoDbTKeyDocumentTestBase<ObjectIdTestDocument, ObjectId>
+    {
+        public override string GetClassName()
+        {
+            return "CRUDObjectIdTests";
+        }
+    }
+}