function Stack() {
	if ( !(this instanceof Stack) ) {
		return new Stack();
	}
	// Use a dynamic array as insertion and deletion is O(1) amortized:
	this._buffer = [];
	return this;
}
Stack constructor.

@constructor
@returns {Stack} stack instance

@example
var s = new Stack();

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

// Remove the top value:
var v = s.pop();
// returns 'bar'

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

// Remove the top value:
v = s.pop();
// returns 'beep'