Review whether boxplot = "identity" and summarise_boxplot_stats are appropriate

[davidhodge931]

list-columns are not very simplevis

Alternative option is to require user to specify: ymin_var ylower_var ymiddle_var yupper_var ymax_var

See pointrange for how this was done

summarise_boxplot_stats could have a boxplot_var_names argument, which could default to:

summarise_boxplot_stats(data, var, var_names = c("min", "lower", "middle", "upper", "max"))

gg_boxplot(data, x_var = blah, ymin_var =min ylower_var = lower ymiddle_var = middle yupper_var = upper ymax_var = max, stat = "identity)