def define(procedure = nil, &block)
      config = Config.new(null: null)
      config.instance_exec(&(procedure || block))
      config.mixin.include Mixin::Root
      config.mixin
    end
def define(procedure = nil, &block)
      config = Config.new(null: null)
      config.instance_exec(&(procedure || block))
      config.mixin.include Mixin::Root
      config.mixin
    end
Returns mixin module to be included to target class by hand
 @return [Module]
 @yield proc defining params and options