Added function to find individual company ticker from CIK value

[webbsledge]

Implement simple function to lookup a ticker for a single CIK value. I didn't see this implemented anywhere already.

[dgunning]

This is probably needed so thanks for this.

2 issues - a cik might have more than one ticker - do you intend to return just the first one?

We also need to handle the case when the ticker is not found so that it does not result in an exception

[webbsledge]

Made some changes to return a list of tickers or a single ticker, depending. Also added some exception handling... hopefully not overkill.

[dgunning]

Looks good. Will integrate and test