coinbase.go
func (c Client) GetBalance() (float64, error) {
	balance := map[string]string{}
	if err := c.Get("account/balance", nil, &balance); err != nil {
		return 0.0, err
	}
	balanceFloat, err := strconv.ParseFloat(balance["amount"], 64)
	if err != nil {
		return 0, err
	}
	return balanceFloat, nil
}
func (c Client) GetBalance() (float64, error) {
	balance := map[string]string{}
	if err := c.Get("account/balance", nil, &balance); err != nil {
		return 0.0, err
	}
	balanceFloat, err := strconv.ParseFloat(balance["amount"], 64)
	if err != nil {
		return 0, err
	}
	return balanceFloat, nil
}
// GetBalance returns current balance in BTC