added ex4.1 ~ 4.2
Merge pull request #9 from Queequeg92/master

static allocator
changed background color suiting for different os
remove exercise on the index
Update README.md
Update README.md
added ex4.3~ex4.19
Merge pull request #10 from Queequeg92/master

change operators of StrBlobPtr

Thx for contribution~
Update template.html
edit css
edit css more
edit more
edited ex4.19
test
ex5_10
Merge pull request #11 from codewyh/My-Branche

ex5_10--Thx for contribution~
ex5_23
ex5_24
ex5_25
error in 5_23