v0.3.1.0 release

  COSBench 0.3.1.0 (13-ww21.3)
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1. revise the fix of inconsistence between snapshot data and report (#18)
2. a few minor enhancement

  COSBench 0.3.0.8 (13-ww20.5)
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1. replace the broken 0.3.0.7 

  COSBench 0.3.0.7 (13-ww20.4)
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1. fix a bug which causes secret key containing "=" doesn't work in s3 adapter (#45)
2. support self-signed certificate for HTTPS (#15)
3. revise the fix for range selector in main stage to (#31)
4. fix a bug which causes inconsistent snapshop data at high concurrency. (#18)

COSBench 0.3.0.1 (13-ww17.5)
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1. add S3 adapter alpha (#36)
2. fix a bug which causes can't login to ceph through swift gateway (#38)
3. support range selector in main stage (#31)