Added SinglyLinkedList & Tests

• Add SinglyLinkedList with push method

• Add Pop to SinglyLinkedList

• Add lessons learned to README

• Add todo methods and snub tests

• Add shift method to SinglyLinkedList

• Add unshift method to SinglyLinkedList class

• Add get method to SinglyLinkedList

• Add link to SinglyLinkedList README

• Add set method to SinglyLinkedList

• Add insert and remove methods to SinglyLinkedList

• Add reverse method to SLL

• Make methods private and remove optional chaining

• Update method names

• Update tests

• Add list v array to README

• Update class to use TS private modifier

• Update tests to utilize beforeEach

Initial Test Release

Nothing to see here.