[Rd] Help useRs to use R's own Time/Date objects more efficiently

[Abby Spurdle]

> (1) Create a top-level help page with a title like "Date and Time
> Classes" to give a brief but general overview. This would mean the
> existing DateTimeClasses would need a new title.

I wanted to modify my first suggestion.
Perhaps a better idea would be to reference an external document
giving an overview of the subject.
I couldn't find a discussion of POSIXct/POSIXlt objects in the R
manuals (unless I missed it somewhere), so perhaps "An Introduction to
R" could be updated to include this subject, and then the help files
could reference that?

Mark Leeds has already mentioned one possible (unofficial) source.
And I suspect that there are others.