calculate_convergence   Calculates convergence based on NMSE
check_predictor_matrix
                        Performs checks on a custom predictor matrix
create_predictor_matrix
                        Creates the default predictor matrix with 0
                        diagonal and 1 elements in the rest.
evaluate_imputation_error
                        Evaluate the imputation error when true values
                        are known.
missForest              Imputes a dataframe and returns imputation
                        models to be used on new observations
missForestPredict       Imputes a new dataframe based on the missForest
                        models
produce_NA              Produces a dataframe with missing values
prop_usable_cases       Calculates variable-wise proportion of usable
                        cases (missing and observed)
