build_news could optionally not add CRAN release date

[jangorecki]

Adding date to CRAN releases in while rendering news/index.html is a nice feature.
Yet if NEWS.md has already those dates in the content, then it makes that information duplicated.
One option is to remove dates from NEWS.md, so news/index.html will have only the one it produces. The downside of it is that readers of NEWS.md directly (not html on pkgdown website) won't have date information available.
Would be useful to have an option in yaml file to disable generation of those dates.

[MichaelChirico]

As noted in this comment, there also seems to be an issue w parsing dates being handled inconsistently:

Rdatatable/data.table#3677 (comment)

Shall I file a separate issue for that?

[yiluheihei]

Add a parameter directly in build_news(add_cran_date = TRUE)? And if the cran dates have been in NEWS.md, set the add_cran_date = FALSE to avoid building duplicated dates.

add_cran_date = TRUE

add_cran_date = FALSE

@hadley What about your opinion?

[hadley]

I think it's better to add parameters to the yaml (so the way pkgdown is run is captured by git), rather than the function.

[yiluheihei]

sounds great, add parameter (e.g. add_cran_date) to _pkgdown_yml to control whether add cran date to the news/index.html

news: 
  - add_cran_date: TRUE

If it's ok, I'll create a pull request

[hadley]

Sounds good, thanks!