#' VirtualTwins : An adapation of VirtualTwins method created by Jared Foster.
#'
#' VirtualTwins is written mainly with reference classes. Briefly, there is three kinds of class :
#' \itemize{
#' \item \code{\link{VT.object}} class to represent RCT dataset used by VirtualTwins. To format correctly RCT dataset, use \code{\link{formatRCTDataset}}.
#' \item \code{\link{VT.difft}} class to compute difference between twins. Family \code{\link{VT.forest}} extends it to compute twins by random forest.
#' \item \code{\link{VT.tree}} class to find subgroups from \code{difft} by CART trees. \code{\link{VT.tree.class}} and \code{\link{VT.tree.reg}} extend it.