Manual page rework

This merge requests includes

• adduser.conf(5): Fix horrible formatting of NOTES section
• all man pages: Convert manpage sources to semantic newlines as recommended by man-pages(7)
• all man pages: Make mandoc -T lint clean
• minor wording changes
• beginning of the manual page rework.

This is the basis for the overdue rework of the manpages, making them ready for translations.

Additional Question: Should the OPTIONS section list the options in alphabetical order?

This is currently work in progress, I will ask for reviews if finished. Likely later today or tomorrow.

Greetings Marc