Update CHANGELOG.md
1. PutPolicy add ReturnUrl etc; 2. GetPolicy.MakeRequest
Merge pull request #53 from xushiwei/feature/resumable-put

1. PutPolicy add ReturnUrl etc; 2. GetPolicy.MakeRequest
rs.MakeBaseUrl
Merge pull request #54 from xushiwei/feature/new-get-api

rs.MakeBaseUrl
api.go
Merge pull request #55 from xushiwei/feature/new-get-api

api.go
CHANGELOG
Merge pull request #57 from xushiwei/feature/new-get-api

CHANGELOG
Merge pull request #56 from qiniu/develop

Release v0.9.1