Implemented IComparable<IRole> on IGuildUser

src/Discord.Net.Core/Extensions/GuildUserExtensions.cs

@@ -22,10 +22,15 @@ namespace Discord
         }
 
         internal static int Compare(this IGuildUser u1, IGuildUser u2) {
+            // These should never be empty since the everyone role is always present
             var r1 = u1.GetRoles().Max();
             var r2 = u2.GetRoles().Max();
             var result = r1.CompareTo(r2);
             return result != 0 ? result : u1.Id.CompareTo(u2.Id);
         }
+
+        internal static int Compare(this IGuildUser user, IRole role) {
+            return user.GetRoles().Max().CompareTo(role);
+        }
     }
 }