v0.7.9

Important change

• Rsquared performance metric for regression/continuous outcomes was previously
  calculated using defaultSummary() function from caret which uses the square
  of Pearson correlation coefficient (r-squared), instead of the correct
  coefficient of determination which is calculated as 1 - rss/tss, where rss =
  residual sum of squares, tss = total sum of squares. The correct formula for
  R-squared is now being applied.

Bugfix

• Prevent bug if x is a single predictor.

Other updates

• Updated documentation.