def load_config(path)
      return unless File.exist?(path)
      buf = File.read(path) 
      eval("#{buf}", binding, path)
    end
def load_config(path)
      return unless File.exist?(path)
      buf = File.read(path) 
      eval("#{buf}", binding, path)
    end
load config file and merge up with the config tree.
 it will not work when the config_path is nil or the file is missed