Simple Linked List Operations.

For a linked list containing strings:

1. Write a function that reads strings typed by the user
   (until the word "end" is typed) and builds those strings
   into a linked list. It does not matter what order those
   strings appear in within the list.

2. Write a function that prints all the strings in a linked
   list.

3. Build those functions into a program that allows them
   to be tested.

   Example run:
       $ a.out
       Type strings, or "end" to end:
       ? one
       ? two
       ? three
       ? four
       ? five
       ? six
       ? end
       You typed six five four three two one
       $

4. Write a function that takes one linked list of strings
   and splits it as exactly as possible into two linked
   lists half the length of the original. This should be
   done efficiently, it only needs one pass through the
   original list.
      Remember that a function can only return one result,
   so you will probably need to design the function with
   three parameters: one for the original list, and two
   reference parameters for the results.
      Make your program test it thoroughly.

5. Write a function that takes two linked list parameters
   and combines them into a single one.
      You should assume that the two linked lists are
   somehow already in alphabetical order. There is no
   need for your program to check. The program does not
   need to work if the incoming lists are not in order.
      The single list that the function produces should
   also have all its strings in alphabetical order.
      Test it thoroughly, make sure it still works properly
   if one or both of the incoming lists are very short or
   even empty. Look at the example below, to make sure the
   combined list is properly in order, you can't just stick
   one list on the end of the other.

   Example run:
       $ a.out
       Shall we test (1) splitting or (2) combining? 2
       Type the first list
       ? zebra
       ? yeti
       ? monkey
       ? emu
       ? bat
       ? end
       You typed bat emu monkey yeti zebra
       Type the first list
       ? pig
       ? llama
       ? frog
       ? ant
       ? end
       You typed ant frog llama pig
       The merged list is ant bat emu frog llama monkey pig yeti zebra
       $