add crc32 check
add UNDEFINED_KEY in io&resumable_io
fix
Merge pull request #31 from SunRunAway/feature/1.0.2&1.0.1

Feature/1.0.2&1.0.1
Merge pull request #33 from SunRunAway/feature/rsf

Feature/rsf
Merge pull request #34 from SunRunAway/feature/v6.0.0_add_UA

feature/v6.0.0 add user-agent
Merge pull request #35 from SunRunAway/feature/fop

Feature/6.0.1 fop
Merge pull request #36 from SunRunAway/feature/docs

add setup.py & CHANGELOG.md
Merge pull request #28 from SunRunAway/feature/1.0.3

Feature/1.0.3
fix conflict