v2.1.0: Remove cost error from metrics

[stephane-caron]

This release removes the cost error from benchmark metrics, and completes the spinning off of test sets to their own repositories. It also brings a few quality-of-use improvements.

Added

• Expose Problem from top-level module
• Link in report header to go to results tables directly
• Number of problems in report header
• Utility function to load a problem from file

Changed

• Breaking: Remove the cost error from benchmark metrics
• Include Python 3.8 in supported versions

Removed

• Move the GitHub Free-for-all test set to its own repository
• Move Maros-Meszaros test set to its own repository

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This discussion was created from the release v2.1.0.