Stash data after market close

[ConradSelig]

Currently even after market close cliStocksTracker will re-download the data for each ticker, despite the fact it hasn't changed. A tmp file should be created at market close to store the last (market) day's data so we don't have to redownload that everytime.

[patrick-hovsepian]

I'd love for the tool to support extended hours and pre market trading data

[ConradSelig]

@patrick-hovsepian see #14. Even then there will still be the overnight hours outside of the pre/post trading where this ticket will come in handy.