Changes to the calculator to make it more robust

[AntwanAbboud]

This is my first issue so i just tried to change something in the first file i saw to improve its functionality. In this case, I made the calculator a bit more robust. Now it can actually work with int, not only float and it doesnt shut down if the incorrect value/key is entered. Furtermore i also added a way for the user to exit the program.

In more detail, the changes i did were:

• I added a method that checked the format of calc results
• Because of this new function, i changed the input to stay as a string instead of converting it to an int
• I changed all returns in other metods to go through "format_result()"
• I added a exception handler for if the input was either not a number or didnt fit with the operator dict
• A way for the user to exit the program buy writing anything other than "y" or "n"