Move from pd.DataReader to py-tidyfinance

[voigtstefan]

In accessing-and-managaging financial data, we still rely on pd.DataReader. I guess we can switch to py-tidyinance altogether here to avoid confusion?

[christophscheuch]

Not sure. We had panda-datareader in the chapter because we used more or less exact the same code in py-tidyfinance. The idea is that we show people how to access data from multiple sources in the book and then package it in tidyfinance for convenience. So imho whatever @dsforecast has implemented instead of pandas-datareader in py-tidyfinance should probably also be in python/accessing-and-managaging-financial-data.

[dsforecast]

I am in favor of ditching pandas_datareader altogether. See pull request #193