Candles: Start and End Time - Wrong Object Call

[SHAHRUKH-KHAN]

The _epoch_millis(start) or _epoch_millis(end) method calls will throw and is throwing attribute error

This happens because the documentation says that start and end should be an integer.

Two Fixes

1. Either Send a datetime object in the
   candles = bitvavo.candles('BTC-EUR', '1h', start = datetime(2024, 8, 10, 9, 30), end = datetime(2024, 8, 10, 9, 40))

2. Just update the _epoch_millis(dt) to return dt*1000 instead of return dt.datetime()*1000. If one sends an integer, this function will always throw an error as mentioned above.