Add_CostBenefit_Axis: Add cost benefit ratio axis to a decision curve plot.
In rmda: Risk Model Decision Analysis

Add cost benefit ratio axis to a decision curve plot.

1 2	Add_CostBenefit_Axis(xlim, cost.benefits, n.cost.benefits = 6, line = 4, policy, ...)

`xlim`	range of x-axis.
`cost.benefits`	Character vector of the form c('c1:b1', 'c2:b2', ..., 'cn:bn') with integers ci, bi corresponding to specific cost:benefit ratios to print.
`n.cost.benefits`	number of cost:benefit ratios to print if cost.benefit.axis = TRUE (default n.cost.benefit = 6).
`line`	x-axis line to print the axis (default is 4).
`policy`	Either 'opt-in' (default) or 'opt-out', describing the type of policy for which to report the net benefit. A policy is 'opt-in' when the standard-of-care for a population is to assign a particular 'treatment' to no one. Clinicians then use a risk model to categorize patients as 'high-risk', with the recommendation to treat high-risk patients with some intervention. Alternatively, an 'opt-out' policy is applicable to contexts where the standard-of-care is to recommend a treatment to an entire patient population. The potential use of a risk model in this setting is to identify patients who are 'low-risk' and recommend that those patients 'opt-out' of treatment.
`...`	other options sent to 'axis'.