docs for "limit upstream tries"
Merge pull request #391 from cfsego/docs

pull request for limiting upstream tries
fix bug described in issue 384, which is about persistent connection in upstream_check_module
Merge pull request #392 from lilbedwin/upstream_check2

fix bug described in issue 384, which is about persistent connection in ...
Auto read nameserver from /etc/resolv.conf.
Merge pull request #390 from lifeibo/resolver

Auto read nameserver from /etc/resolv.conf.
https://github.com/alibaba/tengine/issues/368
Merge pull request #395 from taoyuanyuan/trim

trim module feature and bugfix (https://github.com/alibaba/tengine/issues/368)
Merge branch 'master' of github.com:alibaba/tengine