IEX plugin improvements

[itsankoff]

The PR includes 2 small changes:

1. Put IEX plugin configuration in actual use
2. Implement simple filtering of IEX supported symbols to reduce the amount of gathered data. The current implementation show an example with symbols within SPY

[umitanuki]

Thanks for the interesting patch. I think there are use cases for this. But I don't think hard-coded list of symbol is suitable as a general purpose. Why don't you make it fully configurable to specify which symbols to filter?

[itsankoff]

Sure, I will push the update soon

[itsankoff]

Actually, now I am thinking that you can kind of filtering the symbols if you specify them in the configuration of the iex plugin. But if you want to gather a specific set of symbols the configuration file can grow and become hard to manage.How about implementing filters for NASDAQ sectors:
Aerospace, Auto-Tires-Trucks, Basic Materials, Business Services, Conglomerates, Computers and Technology, Consumer Discretionary, Consumer Staples, Construction, Finance, Industrial Products, Medical, Oils-Energy, Retail-Wholesale, Transportation, Utilities?

[umitanuki]

I agree it's better to specify high-level query term to make it dynamic set of symbols.

[ScottBrenner]

Suggested change

	// SPY is a function which indicates if the given symbols is within S&P500
	// SPY is a function which indicates if the given symbols are within S&P500

[ScottBrenner]

Suggested change

	// SPYSymbols is array symbols which are within S&P500
	// SPYSymbols is an array of symbols which are within S&P500