Stage 8 of 8 for JetBrains Academy Kotlin Smart Calculator project. The program can store values, prioritize with parenthesis, add, subtract, multiply, divide, and exponent given whole numbers from the user. For a stack I used Java's Stack, instead of their stage 7 MutableList suggestion ( for the object Postfix I did make use of a MutableList for storing numbers, and operators popped from the stack - which is then converted to an array when passed back to the SmartCalculator object ).
