MiniZinc Python 0.2.1

Added

• Add support for other command line flags for CLIInstance.flatten()
  through the use of **kwargs.
• Add initial Checker class to allow the usage of MiniZinc solution
  checkers.

Changed

• The string method for Result will now refer to the string method of its
  Solution attribute.

Fixed

• Ensure the event loop selection on Windows to always selects
  ProactorEventLoop. This ensures the usage on Windows when the python
  version <= 3.8.0.