Dwave-cloud-client

New Features
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- `dwave ping` now supports `--sampling-params` argument(s)
- `dwave solvers` now supports listing `--all` solvers independent of solver definition used in config
- `dwave install` now available for contrib packages install
- `dwave setup` introduced to combine `dwave install` and `dwave config create`
- Unstructured solvers will now upload problems prior to sampling by default (using multi-part upload)
- `Future.wait_id` can now be used to block until the submission ID becomes available (i.e. problem is queued)
- Problem answers can now be downloaded from a "cold" session via `Client.retrieve_answer`

Changes
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- Dropped Python 2 support
- Legacy config format deprecated
- Default client class used in config is now "base"

New Features
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- Event subsystem in `dwave.cloud.events` to enable external data capture (early preview)

Fixes
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- Allow `RawIOBase` for file-like input object in `GettableFile`

New Features
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- Multipart problem upload, resilient to network failures, with cold restart (326)
- By-ref problem submit to unstructured solvers (327)
- CLI command for problem upload: `dwave upload`
- Accept custom external HTTP headers in config/env var/`Client` constructor/factory (334)
- Better external log level control (336)

Fixes
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- Thread-safe `requests.Session`s (182)
- Solver graph respected in `dwave ping` on structured solvers (332)
- Correct error handling in `dwave ping` on unstructured solvers (329)