1) Introduction of ncores as extra parameter. 2) Introduction of Calibration as a new function (replacement of .calibration.wrap). 3) removal of var.fc

Handling of case of insufficient data, following the comment of Deborah Verfaillie. The function now warns (and does no calibration) when 3 or less observation-model pairs are available for training. A new parameter na.fill has been introduced.

Speed optimization for mbm_cal method and adaptation for passing of cal.method and eval.method parameters