1. catch ret None issue in rsf.py
2. make param expires optional for GetPolicy in rs/rs_token.py
Add Title for docs/README.md.
fix test
Merge pull request #83 from SunRunAway/develop

fix test
Merge pull request #82 from BluntBlade/develop

Add Title for docs/README.md.
Update rsf.py

``if not ret.get('marker'):`` 在ret为``None``时会报错。
bug fix
fix
Merge pull request #86 from coaku/b_xzk_fix_resumable_upload_bug

bug fix
Merge pull request #84 from Wizmann/patch-1

Update rsf.py
merged develop
Merge pull request #92 from xushiwei/feature/bugfix

Feature/bugfix
rio 4m bug fixed
write 4m content
Merge pull request #93 from dtynn/wanglin/hotfix/rio_4m

rio 4m bug fixed
rewrite
替换文件
fix mime_type typo
Merge pull request #96 from Soniccube/fix_mime_type

fix mime_type typo
update change log