support download private file with downloadtoken
Merge branch 'feature/add_download_token', remote branch 'qiniu/develop' into feature/add_download_token
fix 1st by review suggestions
remove main method
add PutPolicy
to tigger travis
travis build
fixed by review suggestions
fixed 3rd
Merge pull request #35 from wangjinlei/feature/add_download_token

support download private file with downloadtoken