Throttle-by-default examples as well, using \dontshow{} wrapper

[eddelbuettel]

Following the 0.7.0 upload, we now use a helper function to throttle tests as the CRAN Respository Policy says

If running a package uses multiple threads/cores it must never use more than two simultaneously: the check farm is a shared resource and will typically be running many checks simultaneously.

We need to do the same examples, and this PR does that injecting a call to the throttler function, wrapped by \dontshow{} so that it is not displayed in the generated documentation that each example is part of. Help files were then regenerated from R sources via roxygen2. No other changes.