Dimod

Fixes
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* Fix the behavior of the file-like returned by `DQM.to_file`

New Features
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* New parallel constructor for c++ AdjMapBQM
* `DQM.to_file` now returns a seekable file-like
* `DQM.from_numpy_vectors` now reserves the quadratic vectors which should reduce memory and speed up construction

Fixes
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* `DQM.from_file` now correctly accepts bytes-like objects

Changes
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* `DQM.to_file`'s `compressed` kwarg has been deprecated in favor of `compress`

Fixes
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* Support printing sample sets with discrete variables

New Features
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* New `DISCRETE` vartype for sample sets
* `DiscreteQuadraticModel` class
* New parallel constructor for dense c++ BQMs

New Features
------------
* New `DISCRETE` vartype for sample sets

New Features
------------
* `DiscreteQuadraticModel` class
* New parallel constructor for dense c++ BQMs