plot_results.py: prepare plots for font size adjustments

- use relative font sizes in plot_fit_info(), plot_params()
- use tight layout in save_fig()
- plot min. value labels only for non-trivial transforms in plot_fit_info()
ENH: make plot_results.py a full script: new options, main()

- new get_options_parser()
- new --group, --equal-probs, --suffixes, --rc, --show options
ENH: plot_results.py: add plots of non-transformed criteria