code: func (b *Bittrex) GetOrderBookBuySell(market, cat string) (orderb []Orderb, err error) {
  	if cat != "buy" && cat != "sell" {
  		cat = "buy"
  	}
  
  	r, err := b.client.do("GET", fmt.Sprintf("public/getorderbook?market=%s&type=%s", strings.ToUpper(market), cat), "", false)
  	if err != nil {
  		return
  	}
  	var response jsonResponse
  	if err = json.Unmarshal(r, &response); err != nil {
  		return
  	}
  	if err = handleErr(response); err != nil {
  		return
  	}
  	err = json.Unmarshal(response.Result, &orderb)
  	return
  }
docs: // GetOrderBookBuySell is used to get retrieve the buy or sell side of an orderbook for a given market
  // market: a string literal for the market (ex: BTC-LTC)
  // cat: buy or sell to identify the type of orderbook to return.