add In-class Practice of Lecture 3.

The code of In-class Practice of Lecture 2 has been refactored.

The following file was deleted:

	Web.java

replacing by the following 4 files:

	web/Page.java
	web/Weather.java
	web/Web.java
	web/cache/cache.java

Thank you!
							Lawrence X. Amlord
							  Apr 25th, 2014
							  Xi'an, China