Data sources aside from Yahoo

@dpguthrie and I briefly discussed this prospect with @ValueRaider a while back and I find myself considering it again. The quality of Y!Finance data has really gone off of a cliff in the past 6 months. Quarterly earnings data is now very often missing and even tickers with billions in market cap are missing swaths of data. It seems that Yahoo's dedication to their finance product is waning.

Have you guys or anyone else considered expanding yahooquery (at the time I think we were talking about yfinance) to other sources such as Marketwatch? Their data seems to be far more consistent, which makes sense since it's owned by Dow Jones who actually does this as a business.

I suppose the name would have to change from yahooquery ;)

No files, tests, or entry points are named. Start by reviewing the project structure and clarifying which alternative market-data sources and supported data fields are required. Done means there is an agreed source strategy, compatibility scope, and acceptance criteria for replacing or supplementing Yahoo Finance data.

Written by the indexing model from the issue text.