Release 0.2.0

This release of Linfa introduced 9 new implementations and a couple of changes to the APIs. Travis support for FOSS projects was dropped, so we were forced to switch to Github Actions and we introduced a couple of traits to represent different classes of algorithms in a better way.

New algorithms

• Ordinary Linear Regression has been added to linfa-linear by [@Nimpruda] and [@paulkoerbitz]
• Generalized Linear Models has been added to linfa-linear by [@VasanthakumarV]
• Linear decision trees were added to linfa-trees by [@mossbanay]
• Fast independent component analysis (ICA) has been added to linfa-ica by [@VasanthakumarV]
• Principal Component Analysis and Diffusion Maps have been added to linfa-reduction by [@bytesnake]
• Support Vector Machines has been added to linfa-svm by [@bytesnake]
• Logistic regression has been added to linfa-logistic by [@paulkoerbitz]
• Hierarchical agglomerative clustering has been added to linfa-hierarchical by [@bytesnake]
• Gaussian Mixture Models has been added to linfa-clustering by [@relf]

Changes

• Common metrics for classification and regression have been added
• A new dataset interface simplifies the work with targets and labels
• New traits for Transformer, Fit and IncrementalFit standardizes the interface
• Switched to Github Actions for better integration