Place a buy order at market price.

        :param amount: Amount of major currency to buy at market price.
        :type amount: int | float | str | unicode | decimal.Decimal
        :return: Order details.
        :rtype: dict

def buy_market_order(self, amount):
        """Place a buy order at market price.

        :param amount: Amount of major currency to buy at market price.
        :type amount: int | float | str | unicode | decimal.Decimal
        :return: Order details.
        :rtype: dict
        """
        amount = str(amount)
        self._log("buy {} {} at market price".format(amount, self.major))
        return self._rest_client.post(
            endpoint='/buy',
            payload={'book': self.name, 'amount': amount}
        )