release new version for 2.7.1

Merge pull request XX-net#1445 from yeahwu/patch-1

Update README.md

很好的贡献，哈哈

change log

new release 2.6.1, fix bug can't connect after network fail

release 2.6

fix bug: XX-net#1220: div by zero

new release for scan ip problem

fix bug:XX-net#1173, some ip return 200 for HEAD request but can't wo…

…rk as GAE

release 2.5.1 to stable

release new version 2.5.1, fix bug delete good ip