add some functions
1.addAuthor
2.addBook:if the author of book is not existed,the program will ask the
user to add author first.
2.1 add a function:change a book message
it can change a book's title,author,
publisher,publishdate,price
if the author is not existed ,user has to add the author first.
2.1.1
add some text
2.1 fix a bug
fix the bug:when delete some author last book,the information is not
right2.1 fix a bug
fix the bug:when delete some author last book,the information is not right
Merge pull request #1 from yezhejack/2.2

2.2