Update to SDK v0.11.2

[qjiang002]

• Fix import error: use explainaboard.serialization.legacy in SDK 0.11.2

  • Refer to this PR use explainaboard.serialization.legacy in SDK 0.11.2 #334

• conf_value is renamed to confidence_alpha in https://github.com/neulab/ExplainaBoard/pull/475/files

  • conf_value is mapped to confidence_alpha in system_from_dict(). explainaboard_web doesn't use this attribute. It is saved for cache purposes only so this fix makes our code backward compatible.

• float32 and float64 are replaced with float for all Value features in Refactor dtype of Value feature ExplainaBoard#468

  • float32 and float64 are mapped to float in system_from_dict()

• Pre-release Checklist

• Usability Test

• Sequence serialization

  • feature is added to all Sequence objects in Refactor FeatureType ExplainaBoard#462
  • Some information is missing so I can't make it backward compatible. I think we'll need to regenerate all analyses.

[lyuyangh]

Thanks! Could you start a checklist in this issue to document all the breaking changes we need to fix before upgrading to 0.11.2?

[qjiang002]

Sure. I put the two issues so far in the first comment. Feel free to expand this list in the comments!

[lyuyangh]

I'll start working on this if nobody else has started.