mikropml 1.5.0

• New example showing how to plot feature importances in the parallel vignette (#310, @kelly-sovacool).
• You can now use parRF, a parallel implementation of the rf method, with
  the same default hyperparameters as rf set automatically (#306, @kelly-sovacool).
• New functions to calculate and plot ROC and PRC curves: (#321, @kelly-sovacool)
  • calc_model_sensspec() - calculate sensitivity, specificity, and precision for a model.
  • calc_mean_roc() & plot_mean_roc() - calculate & plot specificity and mean sensitivity for multiple models.
  • calc_mean_prc() & plot_mean_prc() - calculate & plot recall and mean precision for multiple models.

Full Changelog: v1.4.0...v1.5.0