Tasks for database build application (ex_build.pl)

[euclidjda]

1. The update prices code should "fill in" all weeks between the current date and the last price date saved.
2. Add free cash flow (fcf_ttm and fcf_4yISm) to the ex_factdata table
3. Add volume data to the ex_prices table
4. Add S&P 500 data to the ex_prices table with special cid = 'SP0500' (maybe)
5. Add code to build ex_fundmts table
6. Add code to build ex_econ table
7. Support ability to go back to early 1970