@Julien: Over your modification that you made, I like all them.
I only will add that in 'generate_package_html.m' should have a use example of package_doc_options field,
or some mentions about that this variable was initialized and the values that it has.
Another thing, I think that
'--css-ref=""
https://www.gnu.org/software/octave/doc/interpreter/octave.css"'
in 'get_html_options.m', should be a relative reference
'--css-ref=""../../octave-forge.css"'
this will help when will be implement a off-line standalone version of the documentation.
(since only would need to be copied the missing files)