mlr3 0.1.7

• Switched to new roxygen2 documentation format for R6 classes.

• resample() and benchmark() now support progress bars via the package
  progressr.

• Row ids now must be numeric. It was previously allowed to have character row
  ids, but this lead to confusion and unnecessary code bloat. Row identifiers
  (e.g., to be used in plots) can still be part of the task, with row role
  "name".

• Row names can now be queried with Task$row_names.

• DataBackendMatrix now supports to store an optional (numeric) dense part.

• Added new method $filter() to filter ResampleResults to a subset of
  iterations.

• Removed deprecated character() -> object converters.

• Empty test sets are now handled separately by learners (#421). An empty
  prediction object is returned for all learners.

• The internal train and predict function of Learner now should be implemented
  as private method: instead of public methods train_internal and
  predict_internal, private methods .train and .predict are now
  encouraged.

• It is now encouraged to move some internal methods from public to private:

  • Learner$train_internal should now be private method $.train.
  • Learner$predict_internal should now be private method $.predict.
  • Measure$score_internal should now be private method $.score.
    The public methods will be deprecated in a future release.

• Removed arguments from the constructor of measures classif.debug and
  classif.costs. These can be set directly by msr().