function FIFO() {
	if ( !(this instanceof FIFO) ) {
		return new FIFO();
	}
	this._length = 0;
	this._first = null;
	this._last = null;
	return this;
}
First-in-first-out queue constructor.

@constructor
@returns {FIFO} FIFO queue instance

@example
var queue = new FIFO();

// Add values to the queue:
queue.push( 'foo' ).push( 'bar' );

// Remove the first value:
var v = queue.pop();
// returns 'foo'

// Add a new value to the queue:
queue.push( 'beep' );

// Remove the "oldest" queue value:
v = queue.pop();
// returns 'bar'