ps queue: Manage a queue of values

This class can be used to manage a FIFO queue (First In First Out) of values like one might manage the stack in the Postscript language.

It can push and pop values from the queue, get the value at the top of the queue or at a given position, get the count of values, exchange the position of two values, duplicate the value at the top of the queue, roll the queue values by a given number of positions.