testex::use_testex_as_testthat() automatic re-documentation?

[dgkf]

Should documentation automatically be generated when testex is run as testthat?

Without re-documenting, there's a risk that tests have been changed, but wouldn't yet be reflected. This is expected if someone is mindful about how testex works, but this is probably not a safe assumption and should probably "just work" in most cases.

Other user-facing behavior ideas:

• Should it rebuild if roxygen2 version is different?
• Should it be configurable? Parameter? DESCRIPTION option?
• Should it overwrite package docs, or just build in a temp folder? Maybe emit a warning if documentation is out of date?