Added string interpolation

Added ability to look for Chance functions in a string and return a interpolated string.

Example:"Dear `title` `last`, It's `hammertime`! You rolled: `rpg('3d10',{\"sum\":true})`! I owe you `dollar()`"
Results:"Dear Dr. Holmes, It's 3938327776797! You rolled: 12! I owe you $1835.50