Merge pull request #77 from chen3feng/develop

Develop
Merge pull request #80 from chen3feng/develop

Cpplint all
Merge pull request #86 from chen3feng/develop

Develop
Merge pull request #87 from chen3feng/develop

cpplint
implement md5 class
delete test.txt
Merge remote-tracking branch 'chen3feng/develop'
use hex encoding, add more testcases
Merge pull request #88 from yeshunping/master

implement md5 class