a list of functions which take a single (mandatory)
argument and returns class label.
newdata
the data to feed to each estimator in estimators
.parallel
a boolean indicating if the predictions should happen in
parallel through estimators. Defaulted to FALSE.
Value
a matrix of predicted responses (either numeric or character, if predictions
are factor variables). The columns corresponds to rows in newdata so
that class-prediction aggregation can be done more effeciently.