doc bug #3562 - fix anchor backlinks and link depths 

':backlinks: top' seemed to be the cause of #3562 , this commit fixes backlinks - they do not point back to #content 
anymore but to the actual anchor link.
 As far as I tested, this does fix the issue, although it might need review with css styling, since css is broken when testing locally.
This commit also fixes depths across all docs, setting the right depths equal to the number of sections.