TDD kata practice

1. RomanToNumberConverter:
   The Kata says you should write a function to convert from Roman Numerals to decimal numerals. In order to keep the kata light, we will not check for valid Roman Numeral. Numbers are formed by combining symbols together and adding the values. Generally, symbols are placed in order of value, starting with the largest values. When smaller values precede larger values, the smaller values are subtracted from the larger values, and the result is added to the total.

   For original problem statement refer: https://github.com/TDD-Katas/roman-numerals