Simplify workflow for updating documentation

[brookslogan]

Migrating from memory of meeting.

Updating just documentation for data objects currently requires:

• Updating docs in epidatasets.
• Re-documenting downstream packages with latest epidatasets, as downstream packages inherit documentation.
• Every developer pulling epidatasets to not reverse doc updates.
• (Maybe some other things? Adjusting version bounds doesn't seem strictly necessary since it's just documentation, but might assist in forcing developers to stay in sync.)

Ideas for simplifying:

• Replace downstream docs with just a single data re-exports topic with links to epidatasets documentation for each object. We get to keep the note about data(<obj name>) (and could add one about needing epidatasets attached for listing its data sets with just data()).
• Remove downstream docs; just @export and that's it. ?/help should route to epidatasets documentation [since we Imports: it], assuming we have identical object naming. We lose the notes about not being able to use data(<obj name>), but that's an dated paradigm anyway, so hopefully not a huge loss.
• Don't re-export at all downstream. This requires adding epidatasets:: and/or library(epidatasets) in various downstream examples and vignettes.

[brookslogan]

I'm trying out the only-@export approach in cmu-delphi/epiprocess#564 because CHECK was complaining about {epiprocess} in the copied documentation. (Trying to parse it as .Rmd stuff.)

[brookslogan]

It's a fight between roxygen2, CHECK, and pkgdown to get something that looks okay and passes all checks. I've ended up with

• an internal re-export topic in epiprocess that I can't seem to get rid of the Format: section in (@format NULL doesn't appear to work)
• direct links to epidatasets in the pkgdown reference