String.join does not exist in java 7. use Joiner instead

Merge branch 'add-elastic1.6-support'

Merge pull request NLPchina#50 from KangYongKyun/master

 ( ( A and B ) or C ) and ( D or E ) case is converted to ( ( A and B) and C ) and ( D or E ). that's wrong

Merge branch 'develop'

update version

UPDATE README and version

update readme

update readme