Initial goal complete.

Program’s original goal is now complete. Calculates user’s GPA either
by simply entering a letter grade and credit hour and has the option to
save the information to a text file.

Updates in this push:
- Try/catch block to catch error when user enters any value other than
integer for credit hour (applies to option 1 or 2)
- save file now saves to user’s home directory, instead of hard coded
into my personal desktop

Future updates - TBA, largely dependent on other features I would like
to add.