Replace `roxygen2::roxygenize()` with `devtools::document()`

[jamesmbaazam]

In the instructions/steps for using devtools here https://github.com/stan-dev/rstantools/blob/99c0d66ae6a78aa10fd16529b0f63c3f3f83e3db/vignettes/minimal-rstan-package.Rmd#L307-L312, you could replace step 3 of using roxygen2::roxygenize() with devtools::document() to keep it pure devtools.

[jgabry]

Thanks. I'm trying to remember if there was some reason we suggested roxygen2::roxygenize(). Does using devtools::document() work fine for you with Stan based packages?

[mcol]

One should potentially be able to use devtools::load_all() at point 1.