Improved Plotting methods

[dewittpe]

At the very least there are three plotting methods that need to be improved.

• plot.cpr_bs
• plot.cpr_cp
• plot.cpr_cn

I would like to build geoms for each object and a default theme as well.

[dewittpe]

See note in commit 66395a3 message

[dewittpe]

Idea: create a ggplot.cpr_cp method then use stat_cp and stat_cp_spline to add the needed layers.