feat: add tz info to all naive datetime object

[ranjanrak]

1> Add IST timezone info to all naive DateTime objects.
Eg: 'order_timestamp': datetime.datetime(2021, 7, 1, 16, 45, 36, tzinfo=tzoffset('Asia/Kolkata', 19800)), 'exchange_timestamp': datetime.datetime(2021, 7, 1, 16, 45, 36, tzinfo=tzoffset('Asia/Kolkata', 19800)
2> Introduce proper logic(is_timestamp) to check if the response string is a timestamp field. Give away with an earlier string length comparison.
3> Add optional mode field for order_margins.
4> Add example with mode param for order_margins.
5> Change the way to handle exceptions for error responses, which don't have the error_type field(MF APIs).
Ex: Kite error response is: {'status': 'error', 'message': "Couldn't find that order_id.", 'data': None, 'error_type': 'GeneralException'}
Where MF error response is: {'status': 'error', 'message': 'Order not found', 'data': {}}. Don't have error_type field in response.

[vividvilla]

Also this will be breaking change so we need to release it as 3.10.0 or 4.0.0, we can decide on this later.