README
Merge pull request #52 from xushiwei/feature/conn

README
refactor some code and fix a legacy of httpclient
update version description
update version in readme
Merge pull request #53 from wangjinlei/feature/fix_httpclient

Feature/fix httpclient
bugfix: http client
CHANGELOG v2.5.1
Merge pull request #55 from xushiwei/feature/v2.5.1

bugfix: http client
Merge pull request #54 from qiniu/develop

Release v2.5.1