```ruby
module Groonga
  module ExpressionRewriters
    @@rewriters = {}

    class << self
      def register(name, rewriter_class)
        @@rewriters[name] = rewriter_class
      end

      def classes
        rewriters_table = Context.instance["rewriters"]
        return [] if rewriters_table.nil?

        rewriters_table.collect do |id|
          record = Record.new(rewriters_table, id)
          name = record.key
          rewriter = @@rewriters[name]
          if rewriter.nil?
            plugin_name = record.plugin_name.value
            require plugin_name
            rewriter = @@rewriters[name]
            raise "unknown rewriter: <#{name}>:<#{plugin_name}>" if rewriter.nil?
          end
          rewriter
        end
      end
    end
  end
end
```

Make expression rewriters table name customizable
user
```ruby
module Groonga
  module ExpressionRewriters
    @@rewriters = {}

    class << self
      def register(name, rewriter_class)
        @@rewriters[name] = rewriter_class
      end

      def classes
        rewriters_table_name = Conf["expression_rewriter.table"] || "rewriters"
        rewriters_table = Context.instance[rewriters_table_name]
        return [] if rewriters_table.nil?

        rewriters_table.collect do |id|
          record = Record.new(rewriters_table, id)
          name = record.key
          rewriter = @@rewriters[name]
          if rewriter.nil?
            plugin_name = record.plugin_name.value
            require plugin_name
            rewriter = @@rewriters[name]
            raise "unknown rewriter: <#{name}>:<#{plugin_name}>" if rewriter.nil?
          end
          rewriter
        end
      end
    end
  end
end
```
assistant