Update my answer to Exercise 3.23.

This is a major update. I've changed the representation of double-ended
queue from ordinary list to doubly linked list. Hence, most of the operaions
has yet changed.

Modified are the following 2 files:

	Exercise_3.23.pdf
	Exercise_3.23.tm

Thank you!
							Lawrence X. Amlord
							  Sept 29th, 2013
							  Xi'an, China