Add Odds Ratio to for categorical variables when using Fisher's Exact

[kmfisch]

Thank you for developing this nice tool! I was wondering it would be possible to include the Odds Ratio as a column in the table when Fisher's Exact test is run on categorical variables. The odds_ratio is calculated in in line 1275 of tableone.py but then it is not returned in line 1286 nor passed through to display in the table. Thank you for your consideration!