Implement Linked List Data Structure

@AshishKnightfury will be implementing linked list

Stuff remaining:
/*
TODO:
    Implement size of linked list
    Implement [ ] operator
    Implement iterator
    Sanitize code using exceptions
*/

This will help: https://solarianprogrammer.com/2019/02/22/cpp-17-implementing-singly-linked-list-smart-pointers/