def depth
      h = get_ssl(@url_public + "/depth")
      {
        "asks"       => h["asks"].map{|a,b| [BigDecimal.new(a.to_s), BigDecimal.new(b.to_s)]}, # to_s でないと誤差が生じる
        "bids"       => h["bids"].map{|a,b| [BigDecimal.new(a.to_s), BigDecimal.new(b.to_s)]}, # to_s でないと誤差が生じる
        "ltimestamp" => Time.now.to_i,
      }
    end
def depth
      h = get_ssl(@url_public + "/depth")
      {
        "asks"       => h["asks"].map{|a,b| [BigDecimal.new(a.to_s), BigDecimal.new(b.to_s)]}, # to_s でないと誤差が生じる
        "bids"       => h["bids"].map{|a,b| [BigDecimal.new(a.to_s), BigDecimal.new(b.to_s)]}, # to_s でないと誤差が生じる
        "ltimestamp" => Time.now.to_i,
      }
    end
Get order book.
 @abstract
 @return [hash] array of market depth
   asks: [Array] 売りオーダー
      price : [BigDecimal]
      size : [BigDecimal]
   bids: [Array] 買いオーダー
      price : [BigDecimal]
      size : [BigDecimal]
   ltimestamp: [int] ローカルタイムスタンプ