Allow filters to redefine Object methods to make them invokable.

lib/liquid/context.rb

@@ -44,21 +44,8 @@ module Liquid
     # for that
     def add_filters(filters)
       filters = [filters].flatten.compact
-      filters.each do |f|
-        raise ArgumentError, "Expected module but got: #{f.class}" unless f.is_a?(Module)
-        Strainer.add_known_filter(f)
-      end
-
-      # If strainer is already setup then there's no choice but to use a runtime
-      # extend call. If strainer is not yet created, we can utilize strainers
-      # cached class based API, which avoids busting the method cache.
-      if @strainer
-        filters.each do |f|
-          strainer.extend(f)
-        end
-      else
-        @filters.concat filters
-      end
+      @filters += filters
+      @strainer = nil
     end
 
     # are there any not handled interrupts?