v0.2.0 - Add metric module and utility module

Release Note for RustyML v0.2.0

Added

• Add train_test_split function in utility module to split dataset for training and dataset for test
• Add function normalized_mutual_info and adjusted_mutual_info to metric module to calculate NMI and AMI info
• Add AUC-ROC value calculation in metric module

Changed

• Change principal_component_analysis module to utility module, change principal_component_analysis_test module to utility_test module
• Keep the algorithm functions in the math module, and move the functions that evaluate the model's performance (such as R-square values) and structures (confusion matrices) to the metric module. Some of them are used in both ways, then keep them in both modules.
• Change the output of some of the functions in math module and metric module from T to Result<T, crate::ModelError>