CUSIP-Ticker remapping

[jblachly]

This addresses issue #10

Caveats: I could not construct a test using existing tests as a template, because these test the output of transaction formatting, etc., whereas this commit modifies the entire output of print_results (indeed, the transformation is done in print_results() because it is the final common pathway of the program).

I did include test fixture data (cusip.ofx) for when a test is constructed; this test data includes a stock/mf transaction, a non-reinvested dividend, and a position.

General comments on structure:

• SecurityList was put in converter.py, but if functionality expanded perhaps deserves its own source file?
• Originally was written to do conversions at point-of-use, but this could become error prone and difficult to maintain as the program expands
• CUrrently, the conversion is done by iterating over the ofx object in the print_results() function. Because txns is a list of references to a subset of ofx.account.statement.transactions, they are automagically modified as well. If this changes, we need to rewrite the conversion process.
• It would be nice if the CUSIP->Ticker remapping could happen at the time of OFX import and probably should be transitioned to this in the future

[egh]

Thanks! This looks good. I have a few things I'd like to change, but I can do this later:

• I'd like to push the mapping down to the conversion layer. This looks pretty easy
• I'd like to remove the option --cusip and just make this the default behavior. I really can't see why the CUSIP would be better than the ticket symbol. The only reason it did that before is because I didn't know what I was doing. :)