generate_html: new characteristic - Adding field (additional documentation:url) to index.html of the online package documentation

[TrucomanX XnamocurT]

I am writing to call your attention and ask for your comments about a pacth that I am proposing.

https://savannah.gnu.org/patch/?8990

My propose is that, the index.html file of reference manual should show a field with a url to a homepage or site with more documentation. By example: videos, examples, tutorials, books, articles and/or theory itself relative to package.

This url should be the site specified in the description file of package.

You can see an example of this modification in the link.

https://savannah.gnu.org/support/download.php?file_id=37069

The link "Additional documentation" is located below the "NEWS" link in the index.html file.

I consider this very important to project packages with a complex theoretical explanation, that need show a bit of theory and some code examples to explain better the use of the package.

The patch can be download of :

https://savannah.gnu.org/support/download.php?file_id=37068

Fernando