def limits(action)
      @limits ||= {}
      limits = @limits[action.to_sym]
      raise TrafficJam::LimitNotFound.new(action) if limits.nil?
      limits
    end
def limits(action)
      @limits ||= {}
      limits = @limits[action.to_sym]
      raise TrafficJam::LimitNotFound.new(action) if limits.nil?
      limits
    end
Get registered limit parameters for an action.

 @see #register
 @param action [Symbol] action name
 @return [Hash] max and period parameters in a hash
 @raise [TrafficJam::LimitNotFound] if action is not registered