Add comments on MLRWorker for algorithm parameters

[yunseong]

In MLRWorker's constructor, there are a lot of parameters for algorithms, but comments are missing. Though the named parameters have their doc (written by @jsjason), it'd be great to see the comments in the constructor (or class) document.

  @Inject
  private MLRWorker(final MLRParser mlrParser,
                    final WorkerSynchronizer synchronizer,
                    final ParameterWorker<Integer, Vector, Vector> worker,
                    @Parameter(NumClasses.class) final int numClasses,
                    @Parameter(NumFeatures.class) final int numFeatures,
                    @Parameter(NumFeaturesPerPartition.class) final int numFeaturesPerPartition,
                    @Parameter(InitialStepSize.class) final double initStepSize,
                    @Parameter(Lambda.class) final double lambda,
                    @Parameter(StatusLogPeriod.class) final int statusLogPeriod,
                    @Parameter(DecayRate.class) final double decayRate,
                    @Parameter(DecayPeriod.class) final int decayPeriod,
                    @Parameter(TrainErrorDatasetSize.class) final int trainErrorDatasetSize,
                    @Parameter(NumBatchPerLossLog.class) final int numBatchPerLossLog,
                    @Parameter(NumBatchPerIter.class) final int numBatchPerIter,
                    @Parameter(AddedEval.class) final boolean addedEval,
                    final DataIdFactory<Long> idFactory,
                    final MemoryStore<Long> memoryStore,
                    final MetricsCollector metricsCollector,
                    final InsertableMetricTracker insertableMetricTracker,
                    final MetricsMessageSender metricsMessageSender,
                    final VectorFactory vectorFactory) {