This is an extension of assignment 3. Make sure that is working properly first.

1. Make your program accept the name of the database file from the command line
   instead of always using /home/218/database.txt, so you might run you program
   by typing
             a.out /home/218/database.txt

2. Add these new commands in your interactive loop:

SAVE filename
   - save the entire database in the named file. Make sure the format is correct,
     you should be able to run your program again, this time giving it the new
     file name, and it being able to read it correctly. Also make sure that when
     you read the saved file, all the deleted people remain deleted.

PRINT
   - print every detail of every person in the database.

SORT NAME
   - sort the database linked list so that the people appear an alphabetical order
     based on their names. Sort primarily on last names, but when two people have
     the same last name, use their first names instead.

SORT AGE
   - sort the database linked list so that the people appear an descending order
     of their ages (i.e. oldest first). If two people have the same birth date,
     it doesn't matter what order they appear in.

     Make sure that whenever you SAVE a sorted database, the people appear in their
     sorted order in the file you create.

KILLZIP zipcode
   - remove everyone who has the given zip code from the database.

Make sure your program's output is neat and tidy. No unnecessary prompts.