Create 07_ExpressionCalculator.cs

07. Write a program that calculates the value of given arithmetical expression. The expression can contain the following elements only:
 - Real numbers, e.g. 5, 18.33, 3.14159, 12.6
 - Arithmetic operators: +, -, *, / (standard priorities)
 - Mathematical functions: ln(x), sqrt(x), pow(x,y)
 - Brackets (for changing the default priorities)
 Examples:
    (3+5.3) * 2.7 - ln(22) / pow(2.2, -1.7) -> ~ 10.6
    pow(2, 3.14) * (3 - (3 * sqrt(2) - 3.2) + 1.5*0.3) -> ~ 21.22
Hint: Use the classical "shunting yard" algorithm and "reverse Polish notation".

Original source for the code below
http://www.dreamincode.net/forums/topic/35320-reverse-polish-notation-in-c%23/
I just replaced some functions and fix two bugs:
   1) On row 142 check if the '-' sign is after closing (right) bracket
   2) On row 302 check and manipulate if there is coma in expression