romanToNum() -- You are to convert from a roman numeral (represented as a string of uppercase letters) to its numerical equivalent. Recall that the roman letters correspond to values as follows: 'M' = 1000, 'D' = 500, 'C' = 100, 'L' = 50, 'X' = 10, 'V' = 5, 'I' = 1. You may assume the ancient roman style of writing letters, where 4 is represented "IIII" and 90 is represented "LXXXX".