CHANGELOG format not compatible between keepachangelog and pkgdown

[TanguyBarthelemy]

I put this issue here because {rjd3toolkit} is the "main" package of the rjd3 package suit.

This issue is strongly related to r-lib/pkgdown#2749.

Our current format is not allowed by pkgdown (which creates the GH pages of our package).

The main problem is that the NEWS.md file won't be rendered in the GH-pages which is a shortfall but not a major one.

Then we have 3 ways of proceeding:

1. we don't care if the NEWS.md is not rendered
2. we accept the pkgdown structure (which follows the tidyverse style guide convention) and so we reject the keep a changelog convention (which is used for all other tools related to JDemetra+
3. we add a small hack during the pkgdown generation of the gh-pages (deletion of the first lines)

What do you think?

[charphi]

Ok, that's annoying.

I think that we should use the third option. I small hack is ok as a temporary solution.
I already have a plan to export keep-a-changelog format to json so it will be easy to create new formats from it.