Extend your solution to assignment 2 so that it is able to delete
strings from the linked list.

When the program is run, it should read string from the user, and
add them to a linked list. Remember that strings are packed four
bytes per word, using the "byte ... of ..." notation. EXCEPT if
the user types DELETE, then the next string should be deleted from
the list rather than added to it. The word DELETE should not be added.

When a word is deleted from the list, the memory it occupies, and
that of the link that contained it, should be recycled using freevec.

When the user types END, the whole list should be printed, and the
program should exit.

Example run:

$ run hw3
Enter the strings and deletions:
hello
this
program
works
properly
DELETE program
dog
cat
DELETE dog
END
hello
this
works
properly
cat
$