LinkedList methods.

[AmirReza-alt]

The LinkedList data structue methods are incomplete.

LinkedLists should have some methode to find indexesor value by the other one.
For example:

• indexOf()
• at()

It also needs a method to print the entire list for the user.

[suman105]

Fix has been implemented and the pull request has been merged. The indexOf(), at(), and the method to print the entire list have been added to the LinkedList class. Thanks for the suggestion!