Blurb::
Perform k-fold cross validation

Description::

General k-fold cross validation may be performed by specifying \c
cross_validation.  The cross-validation statistics will be calculated
for all metrics.

Cross validation may further specify:
\li \c folds, the number of folds into which to divide the build
  data (between 2 and number of data points) or
\li \c percent, the fraction of data (between 0 and 0.5)
  to use in each fold.

These will be adjusted as needed based on the number of available
training points.  The default number of folds k = 10, or 0.1

Topics::	surrogate_models
Examples::
Theory::
Faq::
See_Also::	
