--- merge(other)
--- merge(other) {|key, self_val, other_val| ... }
--- merge!(other)
--- merge!(other) {|key, self_val, other_val| ... }

    ruby 1.8 feature

    Hash#merge ϡhash.dup.update ƱǤ
    Hash#merge! ϡHash#update [Hash/update] ̾Ǥ

