Allow caching of stock data

[Esfo]

Hey thanks for making this, it's super useful.

If possible, I'd like an option that allows for the pulled stock information to be saved locally in a designated folder.

Reloading from cache could prove useful in some scenarios, perhaps such as allowing shorter loading times or if you're without an internet connection and have some kind of curiosity of a historical price.

It would also be great to save some of the data that I'm already collecting anyways, in case I want to backtest some ideas. So instructions for reading the data externally would be worthwhile.

Complementary to this, perhaps introduce a cache size limit for those who might not want to keep infinite data.