def load_XYML io
      raw_yaml=YAML.load(io)
      @root=Xyml.rawobj2element raw_yaml[0]
      self.clear.push @root
      io.close
    end
def load_XYML io
      raw_yaml=YAML.load(io)
      @root=Xyml.rawobj2element raw_yaml[0]
      self.clear.push @root
      io.close
    end
load an XYML file through the designated IO and set the tree data in the file to the self.

 XYMLファイルをIOよりロードして、そのツリーデータを自身に設定する。
      # aaa.xyml
      #  - a:
      #    -b: ccc
      #    -d:
      #      - eee
      xyml_tree=Xyml::Document.new
      xyml_tree.load_XYML(File.open("aaa.xyml"))
      #-> [{a: [{b: "ccc"},{d: ["eee"]}]}]