Standard Scaler

Implemented in `scalers.R`. Uses `cpp_scale_fit_transform` for speed if available, otherwise R `scale`.

fit=function(X){
  X <- as.matrix(X)
  if (exists("cpp_scale_fit_transform", mode="function")) {
    out <- cpp_scale_fit_transform(X)
    mean <<- out$mean
    sd <<- out$sd
  } else {
    mean <<- colMeans(X)
    sd <<- apply(X,2,sd)
    sd[sd==0] <<- 1
  }
}