market_safety: Collects safety z-scores for companies
Description
Given a data frame of companies (names and tickers), a data frame of financial
statements, and a data frame of daily price data, calculates BAB, IVOL, LEV,
O, Z, and EVOL, and determines the z-score of overall safety for each company
based on the paper Quality Minus Junk (Asness et al.) in Appendix page A2.