add ch02 exercise files and change the jQuery js file to common invoke
add single image click invoke math random function to alert
add append function and able to add or remove block
add ch03 file exercise on the ch02 modified basic
another method to realize click bind and unbind show single discount
add single function to handle guess_box show and format js code(ctrl+alt+f)
add get random function hide code function handle whether discount when click
add hover css style when mouse enter and leave these images
add css apend and abount jquery static contains method use