instant pnl should be a percentage of change in the price?

[eugenioclrc]

I think the reward aka instant pnl in the code should be a percentage of change instead of a delta;

https://github.com/Prediction-Machines/Trading-Gym/blob/master/tgym/envs/trading.py#L117
instant_pnl = self._entry_price - self._exit_price

So if we got a very volatile market (like criptos) you will see lower rewards at first and grater rewards at the end, coudl be this a better approach:

instant_pnl = (self._entry_price - self._exit_price) / self._exit_price