Replace xml_converter.py: new converter using lxml

the converter now works with lxml, matching the change in scrape_website, that produces a valid xml now.
also did updates to the readmes and installation guides, plus some stylistic changes. was tested on wind, macos and linux with trafilatura 1.6.1 and promethia (as on 30.8.23)

assigned to @sonja.huber2

marked this merge request as ready

macos actually still has some issues right now with promethia, but the current scrape-script only works with the new converter. Works fine on linux and windows. will fix asap if the issue is on this end.

mentioned in commit 07da08dc

merged