Expressions: Parse, convert and evaluate math expressions

This package can parse, convert and evaluate math expressions.

There is a convertor class that can parse a string with a math expression with infix format (operators in the middle of the operands) to postfix format (operators after operands), as well to expression tree of objects.

An evaluator class can evaluate a math expression from a postfix string or expression or an expression tree of objects.

Currently the evaluation supports addition, subtraction, multiplication and division of integer operator numbers, as well parenthesis to group expressions to be evaluated first.