New Features
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- All SAPI requests retried whenever possible, controlled with new `http_retry_*` Client options (414)
- Introduced `SAPIError` base exception with SAPI error message and code, other exceptions reorganized in a backwards-compatible way
- Support for problem labels: `sample_*` methods accept optional `label` kwarg, and `Future.sampleset.info` contains `problem_label` (444)
- Switched to CircleCI (119)
Fixes
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- Handle remote disconnects in an edge case (229)