* The GPL version was revised to be version 3 (thanks to Ross Quinlan for the note).
* The variable usage statistics were saved to a data frame in called `object$usage`. The package vignette and help files were updated accordingly.
* When using `cubist`, if `x` was a vector or a single variable, an error occurred. This was fixed.
* The vignette was also expanded to show how caret can be used to tune the model and a technical error was corrected about the boosting algorithm (thanks again to Ross Quinlan).