automatically generated changes

I think that these changes happened when I updated the documentation.
Exploring using the `gbm` package from Friedman

The next step will be to compare the outputs of this to `gbm.step` by
Elith et al., as the extra bits and pieces they add may not be needed
anymore.
Simple function for making MCAR data

This is a simple function to make every observation missing with a
probability set by `miss.perc`. This may be useful later, but was
mainly useful for me for a separate paper I was writing.
Tidying up empty space

I believe that this was some tidying of comments.
Added the VignetteEngine code

This code removes the YAML header and replaces it with VigentteEngine,
which I think is needed for official R documentation.