Numerical integration of cause-specific survival curves to arrive at cause-specific cumulative incidence functions,
with three usage modes: 1) Convenient API for parametric survival regression followed by competing-risk analysis, 2) API for
CFC, accepting user-specified survival functions in R, and 3) Same as 2, but accepting survival functions in C++. For
mathematical details and software tutorial, see Mahani and Sharabiani (2019)