Add examples
new file:   ch03/ch03_01/Light.java
new file:   ch03/ch03_02/Area.java
new file:   ch03/ch03_03/CharDemo.java
new file:   ch03/ch03_03/CharDemo2.java
new file:   ch03/ch03_03/CharDemo3.java
new file:   ch03/ch03_04/BoolTest.java