Add a `goal` hyperparameter to Gama base (openml-labs#133)

This lets GAMA automagically configure the AutoML pipeline based on the
user's intent.

Merge pull request openml-labs#115 from PGijsbers/develop

Sync to prepare for new git workflow

Merge pull request openml-labs#100 from PGijsbers/develop

GAMA 20.2.1 release

Merge pull request openml-labs#89 from PGijsbers/develop

Update documentation

🔖 Update version

Merge branch 'develop'

📝 Update doc/conf.

Quick fix for BrokenProcessPool error.

Changed to YY.0M.MICRO versioning scheme.

Revert to scikit-learn 0.19.1.