Update Linked List classes

[phrdang]

Location

• Ch. 16.6 Practice

Changes

• Update and rename LinkedList.java
  • Rename to TestLinkedList.java
  • Add driver class to test methods
  • Update practice problem instructions to be more specific and include driver class
  • Add insert, clear methods
  • Update misc docstrings for clarity
  • Update toString() method to handle empty lists properly
• Delete SinglyLinkedList.java (both practice and solution files)
  • This is a duplicate version of LinkedList.java, but it's implemented and documented more poorly
• Rename the new LinkedList class into SinglyLinkedList to keep consistency with terminology in the curriculum

Notes

• Please don't forget to update the instructions for both LinkedList and SinglyLinkedList on Notion!

TODO

• More methods for the SinglyLinkedList class (e.g. get, set, indexOf)
  • Should we change the method names so that they're closer to the naming of the built-in LinkedList?
• Should we simplify the Node class so that next and value are public? That way you don't have to do the awkward next() and value().
• Add doubly linked list practice problem template and solution
• Add circular linked list practice problem template and solution

[phrdang]

You may want to hold off on merging this PR until Ch. 16 is done being updated. It's a bit all over the place right now in terms of the linked list methods and explanations.