Queue ADT
A queue is a FIFO data structure (i.e. a data structure that retrieves data in the order in which the data is stored)
Items enter the queue at the rear (end of the line) and exit at the front (head of the line)
Basic operations: enqueue, dequeue, len_queue (plus you’ll need constructors, a destructor, and overloaded assignment operator)
Will leave the linked list implementation as an exercise