fixed bug in denominator for Brier score when obs removed for logical cal
   * Fixed inconsistency in predictrms where predict() for Cox models used a design matrix that was centered on medians and modes rather than means (thanks: David van Klaveren <d.vanklaveren.1@erasmusmc.nl>)
   * Added mean absolute prediction error to Rq output
   * Made pr argument passed to predab.resample more encompassing
   * Added more tests for quantile regression and predit