Send a trade history request, return the response.

        Arguements:
        symbol -- currency symbol (default 'btcusd')
        limit_trades -- maximum number of trades to return (default 50)
        timestamp -- only return trades after this unix timestamp (default 0)

def past_trades(self, symbol='btcusd', limit_trades=50, timestamp=0):
        """
        Send a trade history request, return the response.

        Arguements:
        symbol -- currency symbol (default 'btcusd')
        limit_trades -- maximum number of trades to return (default 50)
        timestamp -- only return trades after this unix timestamp (default 0)
        """
        request = '/v1/mytrades'
        url = self.base_url + request
        params = {
            'request': request,
            'nonce': self.get_nonce(),
            'symbol': symbol,
            'limit_trades': limit_trades,
            'timestamp': timestamp
        }

        return requests.post(url, headers=self.prepare(params))