doc: Improve documentation rendering

Add Latex configurations in order to print the copyright in PDF renders.

Remove unnecessary top level section in order to get proper chapter
namings.

Reword sentences specific to HTML vs PDF rendering.

Change the type of the code blocks in the changelog page in order to
work around rendering issues with the PDF target.

Select the "lualatex" engine for Latex as it has shown to be more robust
than the default engine.

Signed-off-by: Ambroise Vincent <ambroise.vincent@arm.com>