Create a class for a stack data structure using linked list.
Stacks class will have push, pop, peek, and isEmpty methods.
Big O for space is O(n) Big o for time is O(n)
- push(value) : will add to the top of the stack
- pop() : will take off whats on top of stack and return that
- peek() : will show whats on top of stack
- isEmpty(): return boolean wheter stack is empty