Update common_ML README with better exposition of methodology

[richardwaynefedorajr]

Add objective functions and code snippets

[richardwaynefedorajr]

condense algorithms into three sections: regression, classifiers, and unsupervised… keep the same basic outputs (e.g. plot of results, confusion/correlation matrix, dataset analysis plots, etc…), but plot all the methods together (like the regression plot is already doing)