[IMPROVE] piotroski stock criteria

[wlemmon]

this seems backward

(https://github.com/JerBouma/FinanceToolkit/blob/b39fa9e111d464a6bff645c0e84eda1bea541baf/financetoolkit/models/piotroski_model.py#L278)

[JerBouma]

Care to elaborate? If it hasn't issued stocks that should be a positive, hence I look at whether it's equal to 0. If it has, the Common Stock Issued would be greater than 0.

[wlemmon]

my mistake, apologies :D i misread the "did not issue common equity" part of the original paper.